"""
It contains the functions to compute the cases that presents an analytical
solutions.
All functions output the analytical solution in kcal/mol
"""
import numpy
from numpy import pi
from scipy import special, linalg
from scipy.misc import factorial
from math import gamma
[docs]def an_spherical(q, xq, E_1, E_2, E_0, R, N):
"""
It computes the analytical solution of the potential of a sphere with
Nq charges inside.
Took from Kirkwood (1934).
Arguments
----------
q : array, charges.
xq : array, positions of the charges.
E_1: float, dielectric constant inside the sphere.
E_2: float, dielectric constant outside the sphere.
E_0: float, dielectric constant of vacuum.
R : float, radius of the sphere.
N : int, number of terms desired in the spherical harmonic expansion.
Returns
--------
PHI: array, reaction potential.
"""
PHI = numpy.zeros(len(q))
for K in range(len(q)):
rho = numpy.sqrt(numpy.sum(xq[K]**2))
zenit = numpy.arccos(xq[K, 2] / rho)
azim = numpy.arctan2(xq[K, 1], xq[K, 0])
phi = 0. + 0. * 1j
for n in range(N):
for m in range(-n, n + 1):
sph1 = special.sph_harm(m, n, zenit, azim)
cons1 = rho**n / (E_1 * E_0 * R**(2 * n + 1)) * (E_1 - E_2) * (
n + 1) / (E_1 * n + E_2 * (n + 1))
cons2 = 4 * pi / (2 * n + 1)
for k in range(len(q)):
rho_k = numpy.sqrt(numpy.sum(xq[k]**2))
zenit_k = numpy.arccos(xq[k, 2] / rho_k)
azim_k = numpy.arctan2(xq[k, 1], xq[k, 0])
sph2 = numpy.conj(special.sph_harm(m, n, zenit_k, azim_k))
phi += cons1 * cons2 * q[K] * rho_k**n * sph1 * sph2
PHI[K] = numpy.real(phi) / (4 * pi)
return PHI
[docs]def get_K(x, n):
"""
It computes the polinomials K needed for Kirkwood-1934 solutions.
K_n(x) in Equation 4 in Kirkwood 1934.
Arguments
----------
x: float, evaluation point of K.
n: int, number of terms desired in the expansion.
Returns
--------
K: float, polinomials K.
"""
K = 0.
n_fact = factorial(n)
n_fact2 = factorial(2 * n)
for s in range(n + 1):
K += 2**s * n_fact * factorial(2 * n - s) / (factorial(s) * n_fact2 *
factorial(n - s)) * x**s
return K
[docs]def an_P(q, xq, E_1, E_2, R, kappa, a, N):
"""
It computes the solvation energy according to Kirkwood-1934.
Arguments
----------
q : array, charges.
xq : array, positions of the charges.
E_1 : float, dielectric constant inside the sphere.
E_2 : float, dielectric constant outside the sphere.
R : float, radius of the sphere.
kappa: float, reciprocal of Debye length.
a : float, radius of the Stern Layer.
N : int, number of terms desired in the polinomial expansion.
Returns
--------
E_P : float, solvation energy.
"""
qe = 1.60217646e-19
Na = 6.0221415e23
E_0 = 8.854187818e-12
cal2J = 4.184
PHI = numpy.zeros(len(q))
for K in range(len(q)):
rho = numpy.sqrt(numpy.sum(xq[K]**2))
zenit = numpy.arccos(xq[K, 2] / rho)
azim = numpy.arctan2(xq[K, 1], xq[K, 0])
phi = 0. + 0. * 1j
for n in range(N):
for m in range(-n, n + 1):
P1 = special.lpmv(numpy.abs(m), n, numpy.cos(zenit))
Enm = 0.
for k in range(len(q)):
rho_k = numpy.sqrt(numpy.sum(xq[k]**2))
zenit_k = numpy.arccos(xq[k, 2] / rho_k)
azim_k = numpy.arctan2(xq[k, 1], xq[k, 0])
P2 = special.lpmv(numpy.abs(m), n, numpy.cos(zenit_k))
Enm += q[k] * rho_k**n * factorial(n - numpy.abs(
m)) / factorial(n + numpy.abs(m)) * P2 * numpy.exp(
-1j * m * azim_k)
C2 = (kappa * a)**2 * get_K(kappa * a, n - 1) / (
get_K(kappa * a, n + 1) + n * (E_2 - E_1) / (
(n + 1) * E_2 + n * E_1) * (R / a)**(2 * n + 1) *
(kappa * a)**2 * get_K(kappa * a, n - 1) / ((2 * n - 1) *
(2 * n + 1)))
C1 = Enm / (E_2 * E_0 * a**
(2 * n + 1)) * (2 * n + 1) / (2 * n - 1) * (E_2 / (
(n + 1) * E_2 + n * E_1))**2
if n == 0 and m == 0:
Bnm = Enm / (E_0 * R) * (
1 / E_2 - 1 / E_1) - Enm * kappa * a / (
E_0 * E_2 * a * (1 + kappa * a))
else:
Bnm = 1. / (E_1 * E_0 * R**(2 * n + 1)) * (E_1 - E_2) * (
n + 1) / (E_1 * n + E_2 * (n + 1)) * Enm - C1 * C2
phi += Bnm * rho**n * P1 * numpy.exp(1j * m * azim)
PHI[K] = numpy.real(phi) / (4 * pi)
C0 = qe**2 * Na * 1e-3 * 1e10 / (cal2J)
E_P = 0.5 * C0 * numpy.sum(q * PHI)
return E_P
[docs]def two_sphere(a, R, kappa, E_1, E_2, q):
"""
It computes the analytical solution of a spherical surface and a spherical
molecule with a center charge, both of radius R.
Follows Cooper&Barba 2016
Arguments
----------
a : float, center to center distance.
R : float, radius of surface and molecule.
kappa: float, reciprocal of Debye length.
E_1 : float, dielectric constant inside the sphere.
E_2 : float, dielectric constant outside the sphere.
q : float, number of qe to be asigned to the charge.
Returns
--------
Einter : float, interaction energy.
E1sphere: float, solvation energy of one sphere.
E2sphere: float, solvation energy of two spheres together.
Note:
Einter should match (E2sphere - 2xE1sphere)
"""
N = 20 # Number of terms in expansion.
qe = 1.60217646e-19
Na = 6.0221415e23
E_0 = 8.854187818e-12
cal2J = 4.184
index2 = numpy.arange(N + 1, dtype=float) + 0.5
index = index2[0:-1]
K1 = special.kv(index2, kappa * a)
K1p = index / (kappa * a) * K1[0:-1] - K1[1:]
k1 = special.kv(index, kappa * a) * numpy.sqrt(pi / (2 * kappa * a))
k1p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * a)**(3 / 2.)) * special.kv(
index, kappa * a) + numpy.sqrt(pi / (2 * kappa * a)) * K1p
I1 = special.iv(index2, kappa * a)
I1p = index / (kappa * a) * I1[0:-1] + I1[1:]
i1 = special.iv(index, kappa * a) * numpy.sqrt(pi / (2 * kappa * a))
i1p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * a)**(3 / 2.)) * special.iv(
index, kappa * a) + numpy.sqrt(pi / (2 * kappa * a)) * I1p
B = numpy.zeros((N, N), dtype=float)
for n in range(N):
for m in range(N):
for nu in range(N):
if n >= nu and m >= nu:
g1 = gamma(n - nu + 0.5)
g2 = gamma(m - nu + 0.5)
g3 = gamma(nu + 0.5)
g4 = gamma(m + n - nu + 1.5)
f1 = factorial(n + m - nu)
f2 = factorial(n - nu)
f3 = factorial(m - nu)
f4 = factorial(nu)
Anm = g1 * g2 * g3 * f1 * (n + m - 2 * nu + 0.5) / (
pi * g4 * f2 * f3 * f4)
kB = special.kv(n + m - 2 * nu + 0.5, kappa *
R) * numpy.sqrt(pi / (2 * kappa * R))
B[n, m] += Anm * kB
M = numpy.zeros((N, N), float)
E_hat = E_1 / E_2
for i in range(N):
for j in range(N):
M[i, j] = (2 * i + 1) * B[i, j] * (
kappa * i1p[i] - E_hat * i * i1[i] / a)
if i == j:
M[i, j] += kappa * k1p[i] - E_hat * i * k1[i] / a
RHS = numpy.zeros(N)
RHS[0] = -E_hat * q / (4 * pi * E_1 * a * a)
a_coeff = linalg.solve(M, RHS)
a0 = a_coeff[0]
a0_inf = -E_hat * q / (4 * pi * E_1 * a * a) * 1 / (kappa * k1p[0])
phi_2 = a0 * k1[0] + i1[0] * numpy.sum(a_coeff * B[:, 0]) - q / (4 * pi *
E_1 * a)
phi_1 = a0_inf * k1[0] - q / (4 * pi * E_1 * a)
phi_inter = phi_2 - phi_1
CC0 = qe**2 * Na * 1e-3 * 1e10 / (cal2J * E_0)
Einter = 0.5 * CC0 * q * phi_inter
E1sphere = 0.5 * CC0 * q * phi_1
E2sphere = 0.5 * CC0 * q * phi_2
return Einter, E1sphere, E2sphere
[docs]def constant_potential_single_point(phi0, a, r, kappa):
"""
It computes the potential in a point 'r' due to a spherical surface
with constant potential phi0, immersed in water. Solution to the
Poisson-Boltzmann problem.
Arguments
----------
phi0 : float, constant potential on the surface of the sphere.
a : float, radius of the sphere.
r : float, distance from the center of the sphere to the evaluation
point.
kappa: float, reciprocal of Debye length.
Returns
--------
phi : float, potential.
"""
phi = a / r * phi0 * numpy.exp(kappa * (a - r))
return phi
[docs]def constant_charge_single_point(sigma0, a, r, kappa, epsilon):
"""
It computes the potential in a point 'r' due to a spherical surface
with constant charge sigma0 immersed in water. Solution to the
Poisson-Boltzmann problem. .
Arguments
----------
sigma0 : float, constant charge on the surface of the sphere.
a : float, radius of the sphere.
r : float, distance from the center of the sphere to the evaluation
point.
kappa : float, reciprocal of Debye length.
epsilon: float, water dielectric constant.
Returns
--------
phi : float, potential.
"""
dphi0 = -sigma0 / epsilon
phi = -dphi0 * a * a / (1 + kappa * a) * numpy.exp(kappa * (a - r)) / r
return phi
[docs]def constant_potential_single_charge(phi0, radius, kappa, epsilon):
"""
It computes the surface charge of a sphere at constant potential, immersed
in water.
Arguments
----------
phi0 : float, constant potential on the surface of the sphere.
radius : float, radius of the sphere.
kappa : float, reciprocal of Debye length.
epsilon: float, water dielectric constant .
Returns
--------
sigma : float, surface charge.
"""
dphi = -phi0 * ((1. + kappa * radius) / radius)
sigma = -epsilon * dphi # Surface charge
return sigma
[docs]def constant_charge_single_potential(sigma0, radius, kappa, epsilon):
"""
It computes the surface potential on a sphere at constant charged, immersed
in water.
Arguments
----------
sigma0 : float, constant charge on the surface of the sphere.
radius : float, radius of the sphere.
kappa : float, reciprocal of Debye length.
epsilon: float, water dielectric constant.
Returns
--------
phi : float, potential.
"""
dphi = -sigma0 / epsilon
phi = -dphi * radius / (1. + kappa * radius) # Surface potential
return phi
[docs]def constant_potential_twosphere(phi01, phi02, r1, r2, R, kappa, epsilon):
"""
It computes the solvation energy of two spheres at constant potential,
immersed in water.
Arguments
----------
phi01 : float, constant potential on the surface of the sphere 1.
phi02 : float, constant potential on the surface of the sphere 2.
r1 : float, radius of sphere 1.
r2 : float, radius of sphere 2.
R : float, distance center to center.
kappa : float, reciprocal of Debye length.
epsilon: float, water dielectric constant.
Returns
--------
E_solv : float, solvation energy.
"""
kT = 4.1419464e-21 # at 300K
qe = 1.60217646e-19
Na = 6.0221415e23
E_0 = 8.854187818e-12
cal2J = 4.184
C0 = kT / qe
phi01 /= C0
phi02 /= C0
k1 = special.kv(0.5, kappa * r1) * numpy.sqrt(pi / (2 * kappa * r1))
k2 = special.kv(0.5, kappa * r2) * numpy.sqrt(pi / (2 * kappa * r2))
B00 = special.kv(0.5, kappa * R) * numpy.sqrt(pi / (2 * kappa * R))
# k1 = special.kv(0.5,kappa*r1)*numpy.sqrt(2/(pi*kappa*r1))
# k2 = special.kv(0.5,kappa*r2)*numpy.sqrt(2/(pi*kappa*r2))
# B00 = special.kv(0.5,kappa*R)*numpy.sqrt(2/(pi*kappa*R))
i1 = special.iv(0.5, kappa * r1) * numpy.sqrt(pi / (2 * kappa * r1))
i2 = special.iv(0.5, kappa * r2) * numpy.sqrt(pi / (2 * kappa * r2))
a0 = (phi02 * B00 * i1 - phi01 * k2) / (B00 * B00 * i2 * i1 - k1 * k2)
b0 = (phi02 * k1 - phi01 * B00 * i2) / (k2 * k1 - B00 * B00 * i1 * i2)
U1 = 2 * pi * phi01 * (phi01 * numpy.exp(kappa * r1) * (kappa * r1) *
(kappa * r1) / numpy.sinh(kappa * r1) - pi * a0 /
(2 * i1))
U2 = 2 * pi * phi02 * (phi02 * numpy.exp(kappa * r2) * (kappa * r2) *
(kappa * r2) / numpy.sinh(kappa * r2) - pi * b0 /
(2 * i2))
print('U1: {}'.format(U1))
print('U2: {}'.format(U2))
print('E: {}'.format(U1 + U2))
C1 = C0 * C0 * epsilon / kappa
u1 = U1 * C1
u2 = U2 * C1
CC0 = qe**2 * Na * 1e-3 * 1e10 / (cal2J * E_0)
E_solv = CC0 * (u1 + u2)
return E_solv
[docs]def constant_potential_twosphere_2(phi01, phi02, r1, r2, R, kappa, epsilon):
"""
It computes the solvation energy of two spheres at constant potential,
immersed in water.
Arguments
----------
phi01 : float, constant potential on the surface of the sphere 1.
phi02 : float, constant potential on the surface of the sphere 2.
r1 : float, radius of sphere 1.
r2 : float, radius of sphere 2.
R : float, distance center to center.
kappa : float, reciprocal of Debye length.
epsilon: float, water dielectric constant.
Returns
--------
E_solv : float, solvation energy.
"""
kT = 4.1419464e-21 # at 300K
qe = 1.60217646e-19
Na = 6.0221415e23
E_0 = 8.854187818e-12
cal2J = 4.184
h = R - r1 - r2
# E_inter = r1*r2*epsilon/(4*R) * ( (phi01+phi02)**2 * log(1+numpy.exp(-kappa*h)) + (phi01-phi02)**2*log(1-numpy.exp(-kappa*h)) )
# E_inter = epsilon*r1*phi01**2/2 * log(1+numpy.exp(-kappa*h))
E_solv = epsilon * r1 * r2 * (phi01**2 + phi02**2) / (4 * (r1 + r2)) * (
(2 * phi01 * phi02) / (phi01**2 + phi02**2) * log(
(1 + numpy.exp(-kappa * h)) /
(1 - numpy.exp(-kappa * h))) + log(1 - numpy.exp(-2 * kappa * h)))
CC0 = qe**2 * Na * 1e-3 * 1e10 / (cal2J * E_0)
E_solv *= CC0
return E_solv
[docs]def constant_potential_single_energy(phi0, r1, kappa, epsilon):
"""
It computes the total energy of a single sphere at constant potential,
inmmersed in water.
Arguments
----------
phi0 : float, constant potential on the surface of the sphere.
r1 : float, radius of sphere.
kappa : float, reciprocal of Debye length.
epsilon: float, water dielectric constant.
Returns
--------
E : float, total energy.
"""
N = 1 # Number of terms in expansion
qe = 1.60217646e-19
Na = 6.0221415e23
E_0 = 8.854187818e-12
cal2J = 4.184
index2 = numpy.arange(N + 1, dtype=float) + 0.5
index = index2[0:-1]
K1 = special.kv(index2, kappa * r1)
K1p = index / (kappa * r1) * K1[0:-1] - K1[1:]
k1 = special.kv(index, kappa * r1) * numpy.sqrt(pi / (2 * kappa * r1))
k1p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r1)**(3 / 2.)) * special.kv(
index, kappa * r1) + numpy.sqrt(pi / (2 * kappa * r1)) * K1p
a0_inf = phi0 / k1[0]
U1_inf = a0_inf * k1p[0]
C1 = 2 * pi * kappa * phi0 * r1 * r1 * epsilon
C0 = qe**2 * Na * 1e-3 * 1e10 / (cal2J * E_0)
E = C0 * C1 * U1_inf
return E
[docs]def constant_charge_single_energy(sigma0, r1, kappa, epsilon):
"""
It computes the total energy of a single sphere at constant charge,
inmmersed in water.
Arguments
----------
sigma0 : float, constant charge on the surface of the sphere.
r1 : float, radius of sphere.
kappa : float, reciprocal of Debye length.
epsilon: float, water dielectric constant.
Returns
--------
E : float, total energy.
"""
N = 20 # Number of terms in expansion
qe = 1.60217646e-19
Na = 6.0221415e23
E_0 = 8.854187818e-12
cal2J = 4.184
index2 = numpy.arange(N + 1, dtype=float) + 0.5
index = index2[0:-1]
K1 = special.kv(index2, kappa * r1)
K1p = index / (kappa * r1) * K1[0:-1] - K1[1:]
k1 = special.kv(index, kappa * r1) * numpy.sqrt(pi / (2 * kappa * r1))
k1p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r1)**(3 / 2.)) * special.kv(
index, kappa * r1) + numpy.sqrt(pi / (2 * kappa * r1)) * K1p
a0_inf = -sigma0 / (epsilon * kappa * k1p[0])
U1_inf = a0_inf * k1[0]
C1 = 2 * pi * sigma0 * r1 * r1
C0 = qe**2 * Na * 1e-3 * 1e10 / (cal2J * E_0)
E = C0 * C1 * U1_inf
return E
[docs]def constant_potential_twosphere_dissimilar(phi01, phi02, r1, r2, R, kappa,
epsilon):
"""
It computes the interaction energy for dissimilar spheres at constant
potential, immersed in water.
Arguments
----------
phi01 : float, constant potential on the surface of the sphere 1.
phi02 : float, constant potential on the surface of the sphere 2.
r1 : float, radius of sphere 1.
r2 : float, radius of sphere 2.
R : float, distance center to center.
kappa : float, reciprocal of Debye length.
epsilon: float, water dielectric constant.
Returns
--------
E_inter: float, interaction energy.
"""
N = 20 # Number of terms in expansion
qe = 1.60217646e-19
Na = 6.0221415e23
E_0 = 8.854187818e-12
cal2J = 4.184
index2 = numpy.arange(N + 1, dtype=float) + 0.5
index = index2[0:-1]
K1 = special.kv(index2, kappa * r1)
K1p = index / (kappa * r1) * K1[0:-1] - K1[1:]
k1 = special.kv(index, kappa * r1) * numpy.sqrt(pi / (2 * kappa * r1))
k1p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r1)**(3 / 2.)) * special.kv(
index, kappa * r1) + numpy.sqrt(pi / (2 * kappa * r1)) * K1p
K2 = special.kv(index2, kappa * r2)
K2p = index / (kappa * r2) * K2[0:-1] - K2[1:]
k2 = special.kv(index, kappa * r2) * numpy.sqrt(pi / (2 * kappa * r2))
k2p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r2)**(3 / 2.)) * special.kv(
index, kappa * r2) + numpy.sqrt(pi / (2 * kappa * r2)) * K2p
I1 = special.iv(index2, kappa * r1)
I1p = index / (kappa * r1) * I1[0:-1] + I1[1:]
i1 = special.iv(index, kappa * r1) * numpy.sqrt(pi / (2 * kappa * r1))
i1p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r1)**(3 / 2.)) * special.iv(
index, kappa * r1) + numpy.sqrt(pi / (2 * kappa * r1)) * I1p
I2 = special.iv(index2, kappa * r2)
I2p = index / (kappa * r2) * I2[0:-1] + I2[1:]
i2 = special.iv(index, kappa * r2) * numpy.sqrt(pi / (2 * kappa * r2))
i2p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r2)**(3 / 2.)) * special.iv(
index, kappa * r2) + numpy.sqrt(pi / (2 * kappa * r2)) * I2p
B = numpy.zeros((N, N), dtype=float)
for n in range(N):
for m in range(N):
for nu in range(N):
if n >= nu and m >= nu:
g1 = gamma(n - nu + 0.5)
g2 = gamma(m - nu + 0.5)
g3 = gamma(nu + 0.5)
g4 = gamma(m + n - nu + 1.5)
f1 = factorial(n + m - nu)
f2 = factorial(n - nu)
f3 = factorial(m - nu)
f4 = factorial(nu)
Anm = g1 * g2 * g3 * f1 * (n + m - 2 * nu + 0.5) / (
pi * g4 * f2 * f3 * f4)
kB = special.kv(n + m - 2 * nu + 0.5, kappa *
R) * numpy.sqrt(pi / (2 * kappa * R))
B[n, m] += Anm * kB
M = numpy.zeros((2 * N, 2 * N), float)
for j in range(N):
for n in range(N):
M[j, n + N] = (2 * j + 1) * B[j, n] * i1[j] / k2[n]
M[j + N, n] = (2 * j + 1) * B[j, n] * i2[j] / k1[n]
if n == j:
M[j, n] = 1
M[j + N, n + N] = 1
RHS = numpy.zeros(2 * N)
RHS[0] = phi01
RHS[N] = phi02
coeff = linalg.solve(M, RHS)
a = coeff[0:N] / k1
b = coeff[N:2 * N] / k2
a0 = a[0]
a0_inf = phi01 / k1[0]
b0 = b[0]
b0_inf = phi02 / k2[0]
U1_inf = a0_inf * k1p[0]
U1_h = a0 * k1p[0] + i1p[0] * numpy.sum(b * B[:, 0])
U2_inf = b0_inf * k2p[0]
U2_h = b0 * k2p[0] + i2p[0] * numpy.sum(a * B[:, 0])
C1 = 2 * pi * kappa * phi01 * r1 * r1 * epsilon
C2 = 2 * pi * kappa * phi02 * r2 * r2 * epsilon
C0 = qe**2 * Na * 1e-3 * 1e10 / (cal2J * E_0)
E_inter = C0 * (C1 * (U1_h - U1_inf) + C2 * (U2_h - U2_inf))
return E_inter
[docs]def constant_charge_twosphere_dissimilar(sigma01, sigma02, r1, r2, R, kappa,
epsilon):
"""
It computes the interaction energy between two dissimilar spheres at
constant charge, immersed in water.
Arguments
----------
sigma01: float, constant charge on the surface of the sphere 1.
sigma02: float, constant charge on the surface of the sphere 2.
r1 : float, radius of sphere 1.
r2 : float, radius of sphere 2.
R : float, distance center to center.
kappa : float, reciprocal of Debye length.
epsilon: float, water dielectric constant.
Returns
--------
E_inter: float, interaction energy.
"""
N = 20 # Number of terms in expansion
qe = 1.60217646e-19
Na = 6.0221415e23
E_0 = 8.854187818e-12
cal2J = 4.184
index2 = numpy.arange(N + 1, dtype=float) + 0.5
index = index2[0:-1]
K1 = special.kv(index2, kappa * r1)
K1p = index / (kappa * r1) * K1[0:-1] - K1[1:]
k1 = special.kv(index, kappa * r1) * numpy.sqrt(pi / (2 * kappa * r1))
k1p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r1)**(3 / 2.)) * special.kv(
index, kappa * r1) + numpy.sqrt(pi / (2 * kappa * r1)) * K1p
K2 = special.kv(index2, kappa * r2)
K2p = index / (kappa * r2) * K2[0:-1] - K2[1:]
k2 = special.kv(index, kappa * r2) * numpy.sqrt(pi / (2 * kappa * r2))
k2p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r2)**(3 / 2.)) * special.kv(
index, kappa * r2) + numpy.sqrt(pi / (2 * kappa * r2)) * K2p
I1 = special.iv(index2, kappa * r1)
I1p = index / (kappa * r1) * I1[0:-1] + I1[1:]
i1 = special.iv(index, kappa * r1) * numpy.sqrt(pi / (2 * kappa * r1))
i1p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r1)**(3 / 2.)) * special.iv(
index, kappa * r1) + numpy.sqrt(pi / (2 * kappa * r1)) * I1p
I2 = special.iv(index2, kappa * r2)
I2p = index / (kappa * r2) * I2[0:-1] + I2[1:]
i2 = special.iv(index, kappa * r2) * numpy.sqrt(pi / (2 * kappa * r2))
i2p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r2)**(3 / 2.)) * special.iv(
index, kappa * r2) + numpy.sqrt(pi / (2 * kappa * r2)) * I2p
B = numpy.zeros((N, N), dtype=float)
for n in range(N):
for m in range(N):
for nu in range(N):
if n >= nu and m >= nu:
g1 = gamma(n - nu + 0.5)
g2 = gamma(m - nu + 0.5)
g3 = gamma(nu + 0.5)
g4 = gamma(m + n - nu + 1.5)
f1 = factorial(n + m - nu)
f2 = factorial(n - nu)
f3 = factorial(m - nu)
f4 = factorial(nu)
Anm = g1 * g2 * g3 * f1 * (n + m - 2 * nu + 0.5) / (
pi * g4 * f2 * f3 * f4)
kB = special.kv(n + m - 2 * nu + 0.5, kappa *
R) * numpy.sqrt(pi / (2 * kappa * R))
B[n, m] += Anm * kB
M = numpy.zeros((2 * N, 2 * N), float)
for j in range(N):
for n in range(N):
M[j, n + N] = (2 * j + 1) * B[j, n] * r1 * i1p[j] / (r2 * k2p[n])
M[j + N, n] = (2 * j + 1) * B[j, n] * r2 * i2p[j] / (r1 * k1p[n])
if n == j:
M[j, n] = 1
M[j + N, n + N] = 1
RHS = numpy.zeros(2 * N)
RHS[0] = sigma01 * r1 / epsilon
RHS[N] = sigma02 * r2 / epsilon
coeff = linalg.solve(M, RHS)
a = coeff[0:N] / (-r1 * kappa * k1p)
b = coeff[N:2 * N] / (-r2 * kappa * k2p)
a0 = a[0]
a0_inf = -sigma01 / (epsilon * kappa * k1p[0])
b0 = b[0]
b0_inf = -sigma02 / (epsilon * kappa * k2p[0])
U1_inf = a0_inf * k1[0]
U1_h = a0 * k1[0] + i1[0] * numpy.sum(b * B[:, 0])
U2_inf = b0_inf * k2[0]
U2_h = b0 * k2[0] + i2[0] * numpy.sum(a * B[:, 0])
C1 = 2 * pi * sigma01 * r1 * r1
C2 = 2 * pi * sigma02 * r2 * r2
C0 = qe**2 * Na * 1e-3 * 1e10 / (cal2J * E_0)
E_inter = C0 * (C1 * (U1_h - U1_inf) + C2 * (U2_h - U2_inf))
return E_inter
[docs]def molecule_constant_potential(q, phi02, r1, r2, R, kappa, E_1, E_2):
"""
It computes the interaction energy between a molecule (sphere with
point-charge in the center) and a sphere at constant potential, immersed
in water.
Arguments
----------
q : float, number of qe to be asigned to the charge.
phi02 : float, constant potential on the surface of the sphere 2.
r1 : float, radius of sphere 1, i.e the molecule.
r2 : float, radius of sphere 2.
R : float, distance center to center.
kappa : float, reciprocal of Debye length.
E_1 : float, dielectric constant inside the sphere/molecule.
E_2 : float, dielectric constant outside the sphere/molecule.
Returns
--------
E_inter: float, interaction energy.
"""
N = 20 # Number of terms in expansion
qe = 1.60217646e-19
Na = 6.0221415e23
E_0 = 8.854187818e-12
cal2J = 4.184
index2 = numpy.arange(N + 1, dtype=float) + 0.5
index = index2[0:-1]
K1 = special.kv(index2, kappa * r1)
K1p = index / (kappa * r1) * K1[0:-1] - K1[1:]
k1 = special.kv(index, kappa * r1) * numpy.sqrt(pi / (2 * kappa * r1))
k1p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r1)**(3 / 2.)) * special.kv(
index, kappa * r1) + numpy.sqrt(pi / (2 * kappa * r1)) * K1p
K2 = special.kv(index2, kappa * r2)
K2p = index / (kappa * r2) * K2[0:-1] - K2[1:]
k2 = special.kv(index, kappa * r2) * numpy.sqrt(pi / (2 * kappa * r2))
k2p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r2)**(3 / 2.)) * special.kv(
index, kappa * r2) + numpy.sqrt(pi / (2 * kappa * r2)) * K2p
I1 = special.iv(index2, kappa * r1)
I1p = index / (kappa * r1) * I1[0:-1] + I1[1:]
i1 = special.iv(index, kappa * r1) * numpy.sqrt(pi / (2 * kappa * r1))
i1p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r1)**(3 / 2.)) * special.iv(
index, kappa * r1) + numpy.sqrt(pi / (2 * kappa * r1)) * I1p
I2 = special.iv(index2, kappa * r2)
I2p = index / (kappa * r2) * I2[0:-1] + I2[1:]
i2 = special.iv(index, kappa * r2) * numpy.sqrt(pi / (2 * kappa * r2))
i2p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r2)**(3 / 2.)) * special.iv(
index, kappa * r2) + numpy.sqrt(pi / (2 * kappa * r2)) * I2p
B = numpy.zeros((N, N), dtype=float)
for n in range(N):
for m in range(N):
for nu in range(N):
if n >= nu and m >= nu:
g1 = gamma(n - nu + 0.5)
g2 = gamma(m - nu + 0.5)
g3 = gamma(nu + 0.5)
g4 = gamma(m + n - nu + 1.5)
f1 = factorial(n + m - nu)
f2 = factorial(n - nu)
f3 = factorial(m - nu)
f4 = factorial(nu)
Anm = g1 * g2 * g3 * f1 * (n + m - 2 * nu + 0.5) / (
pi * g4 * f2 * f3 * f4)
kB = special.kv(n + m - 2 * nu + 0.5, kappa *
R) * numpy.sqrt(pi / (2 * kappa * R))
B[n, m] += Anm * kB
E_hat = E_1 / E_2
M = numpy.zeros((2 * N, 2 * N), float)
for j in range(N):
for n in range(N):
M[j, n + N] = (2 * j + 1) * B[j, n] * (
kappa * i1p[j] / k2[n] - E_hat * j / r1 * i1[j] / k2[n])
M[j + N, n] = (2 * j + 1) * B[j, n] * i2[j] * 1 / (
kappa * k1p[n] - E_hat * n / r1 * k1[n])
if n == j:
M[j, n] = 1
M[j + N, n + N] = 1
RHS = numpy.zeros(2 * N)
RHS[0] = -E_hat * q / (4 * pi * E_1 * r1 * r1)
RHS[N] = phi02
coeff = linalg.solve(M, RHS)
a = coeff[0:N] / (kappa * k1p - E_hat * numpy.arange(N) / r1 * k1)
b = coeff[N:2 * N] / k2
a0 = a[0]
a0_inf = -E_hat * q / (4 * pi * E_1 * r1 * r1) * 1 / (kappa * k1p[0])
b0 = b[0]
b0_inf = phi02 / k2[0]
phi_inf = a0_inf * k1[0] - q / (4 * pi * E_1 * r1)
phi_h = a0 * k1[0] + i1[0] * numpy.sum(b * B[:, 0]) - q / (4 * pi * E_1 *
r1)
phi_inter = phi_h - phi_inf
U_inf = b0_inf * k2p[0]
U_h = b0 * k2p[0] + i2p[0] * numpy.sum(a * B[:, 0])
U_inter = U_h - U_inf
C0 = qe**2 * Na * 1e-3 * 1e10 / (cal2J * E_0)
C1 = q * 0.5
C2 = 2 * pi * kappa * phi02 * r2 * r2 * E_2
E_inter = C0 * (C1 * phi_inter + C2 * U_inter)
return E_inter
[docs]def molecule_constant_charge(q, sigma02, r1, r2, R, kappa, E_1, E_2):
"""
It computes the interaction energy between a molecule (sphere with
point-charge in the center) and a sphere at constant charge, immersed
in water.
Arguments
----------
q : float, number of qe to be asigned to the charge.
sigma02: float, constant charge on the surface of the sphere 2.
r1 : float, radius of sphere 1, i.e the molecule.
r2 : float, radius of sphere 2.
R : float, distance center to center.
kappa : float, reciprocal of Debye length.
E_1 : float, dielectric constant inside the sphere/molecule.
E_2 : float, dielectric constant outside the sphere/molecule.
Returns
--------
E_inter: float, interaction energy.
"""
N = 20 # Number of terms in expansion
qe = 1.60217646e-19
Na = 6.0221415e23
E_0 = 8.854187818e-12
cal2J = 4.184
index2 = numpy.arange(N + 1, dtype=float) + 0.5
index = index2[0:-1]
K1 = special.kv(index2, kappa * r1)
K1p = index / (kappa * r1) * K1[0:-1] - K1[1:]
k1 = special.kv(index, kappa * r1) * numpy.sqrt(pi / (2 * kappa * r1))
k1p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r1)**(3 / 2.)) * special.kv(
index, kappa * r1) + numpy.sqrt(pi / (2 * kappa * r1)) * K1p
K2 = special.kv(index2, kappa * r2)
K2p = index / (kappa * r2) * K2[0:-1] - K2[1:]
k2 = special.kv(index, kappa * r2) * numpy.sqrt(pi / (2 * kappa * r2))
k2p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r2)**(3 / 2.)) * special.kv(
index, kappa * r2) + numpy.sqrt(pi / (2 * kappa * r2)) * K2p
I1 = special.iv(index2, kappa * r1)
I1p = index / (kappa * r1) * I1[0:-1] + I1[1:]
i1 = special.iv(index, kappa * r1) * numpy.sqrt(pi / (2 * kappa * r1))
i1p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r1)**(3 / 2.)) * special.iv(
index, kappa * r1) + numpy.sqrt(pi / (2 * kappa * r1)) * I1p
I2 = special.iv(index2, kappa * r2)
I2p = index / (kappa * r2) * I2[0:-1] + I2[1:]
i2 = special.iv(index, kappa * r2) * numpy.sqrt(pi / (2 * kappa * r2))
i2p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * r2)**(3 / 2.)) * special.iv(
index, kappa * r2) + numpy.sqrt(pi / (2 * kappa * r2)) * I2p
B = numpy.zeros((N, N), dtype=float)
for n in range(N):
for m in range(N):
for nu in range(N):
if n >= nu and m >= nu:
g1 = gamma(n - nu + 0.5)
g2 = gamma(m - nu + 0.5)
g3 = gamma(nu + 0.5)
g4 = gamma(m + n - nu + 1.5)
f1 = factorial(n + m - nu)
f2 = factorial(n - nu)
f3 = factorial(m - nu)
f4 = factorial(nu)
Anm = g1 * g2 * g3 * f1 * (n + m - 2 * nu + 0.5) / (
pi * g4 * f2 * f3 * f4)
kB = special.kv(n + m - 2 * nu + 0.5, kappa *
R) * numpy.sqrt(pi / (2 * kappa * R))
B[n, m] += Anm * kB
E_hat = E_1 / E_2
M = numpy.zeros((2 * N, 2 * N), float)
for j in range(N):
for n in range(N):
M[j, n + N] = (2 * j + 1) * B[j, n] * (
i1p[j] / k2p[n] - E_hat * j / r1 * i1[j] / (kappa * k2p[n]))
M[j + N, n] = (2 * j + 1) * B[j, n] * i2p[j] * kappa * 1 / (
kappa * k1p[n] - E_hat * n / r1 * k1[n])
if n == j:
M[j, n] = 1
M[j + N, n + N] = 1
RHS = numpy.zeros(2 * N)
RHS[0] = -E_hat * q / (4 * pi * E_1 * r1 * r1)
RHS[N] = -sigma02 / E_2
coeff = linalg.solve(M, RHS)
a = coeff[0:N] / (kappa * k1p - E_hat * numpy.arange(N) / r1 * k1)
b = coeff[N:2 * N] / (kappa * k2p)
a0 = a[0]
a0_inf = -E_hat * q / (4 * pi * E_1 * r1 * r1) * 1 / (kappa * k1p[0])
b0 = b[0]
b0_inf = -sigma02 / (E_2 * kappa * k2p[0])
phi_inf = a0_inf * k1[0] - q / (4 * pi * E_1 * r1)
phi_h = a0 * k1[0] + i1[0] * numpy.sum(b * B[:, 0]) - q / (4 * pi * E_1 *
r1)
phi_inter = phi_h - phi_inf
U_inf = b0_inf * k2[0]
U_h = b0 * k2[0] + i2[0] * numpy.sum(a * B[:, 0])
U_inter = U_h - U_inf
C0 = qe**2 * Na * 1e-3 * 1e10 / (cal2J * E_0)
C1 = q * 0.5
C2 = 2 * pi * sigma02 * r2 * r2
E_inter = C0 * (C1 * phi_inter + C2 * U_inter)
return E_inter
[docs]def constant_potential_twosphere_identical(phi01, phi02, r1, r2, R, kappa,
epsilon):
"""
It computes the interaction energy for two spheres at constants surface
potential, according to Carnie&Chan-1993.
Arguments
----------
phi01 : float, constant potential on the surface of the sphere 1.
phi02 : float, constant potential on the surface of the sphere 2.
r1 : float, radius of sphere 1.
r2 : float, radius of sphere 2.
R : float, distance center to center.
kappa : float, reciprocal of Debye length.
epsilon: float, water dielectric constant.
Note:
Even though it admits phi01 and phi02, they should be identical; and
the same is applicable to r1 and r2.
Returns
--------
E_inter: float, interaction energy.
"""
# From Carnie+Chan 1993
N = 20 # Number of terms in expansion
qe = 1.60217646e-19
Na = 6.0221415e23
E_0 = 8.854187818e-12
cal2J = 4.184
index = numpy.arange(N, dtype=float) + 0.5
k1 = special.kv(index, kappa * r1) * numpy.sqrt(pi / (2 * kappa * r1))
k2 = special.kv(index, kappa * r2) * numpy.sqrt(pi / (2 * kappa * r2))
i1 = special.iv(index, kappa * r1) * numpy.sqrt(pi / (2 * kappa * r1))
i2 = special.iv(index, kappa * r2) * numpy.sqrt(pi / (2 * kappa * r2))
B = numpy.zeros((N, N), dtype=float)
for n in range(N):
for m in range(N):
for nu in range(N):
if n >= nu and m >= nu:
g1 = gamma(n - nu + 0.5)
g2 = gamma(m - nu + 0.5)
g3 = gamma(nu + 0.5)
g4 = gamma(m + n - nu + 1.5)
f1 = factorial(n + m - nu)
f2 = factorial(n - nu)
f3 = factorial(m - nu)
f4 = factorial(nu)
Anm = g1 * g2 * g3 * f1 * (n + m - 2 * nu + 0.5) / (
pi * g4 * f2 * f3 * f4)
kB = special.kv(n + m - 2 * nu + 0.5, kappa *
R) * numpy.sqrt(pi / (2 * kappa * R))
B[n, m] += Anm * kB
M = numpy.zeros((N, N), float)
for i in range(N):
for j in range(N):
M[i, j] = (2 * i + 1) * B[i, j] * i1[i]
if i == j:
M[i, j] += k1[i]
RHS = numpy.zeros(N)
RHS[0] = phi01
a = linalg.solve(M, RHS)
a0 = a[0]
U = 4 * pi * (-pi / 2 * a0 / phi01 * 1 / numpy.sinh(kappa * r1) + kappa *
r1 + kappa * r1 / numpy.tanh(kappa * r1))
C0 = qe**2 * Na * 1e-3 * 1e10 / (cal2J * E_0)
C1 = r1 * epsilon * phi01 * phi01
E_inter = U * C1 * C0
return E_inter
[docs]def constant_charge_twosphere_identical(sigma, a, R, kappa, epsilon):
"""
It computes the interaction energy for two spheres at constants surface
charge, according to Carnie&Chan-1993.
Arguments
----------
sigma : float, constant charge on the surface of the spheres.
a : float, radius of spheres.
R : float, distance center to center.
kappa : float, reciprocal of Debye length.
epsilon: float, water dielectric constant.
Returns
--------
E_inter: float, interaction energy.
"""
# From Carnie+Chan 1993
N = 10 # Number of terms in expansion
E_p = 0 # Permitivitty inside sphere
qe = 1.60217646e-19
Na = 6.0221415e23
E_0 = 8.854187818e-12
cal2J = 4.184
index2 = numpy.arange(N + 1, dtype=float) + 0.5
index = index2[0:-1]
K1 = special.kv(index2, kappa * a)
K1p = index / (kappa * a) * K1[0:-1] - K1[1:]
k1 = special.kv(index, kappa * a) * numpy.sqrt(pi / (2 * kappa * a))
k1p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * a)**(3 / 2.)) * special.kv(
index, kappa * a) + numpy.sqrt(pi / (2 * kappa * a)) * K1p
I1 = special.iv(index2, kappa * a)
I1p = index / (kappa * a) * I1[0:-1] + I1[1:]
i1 = special.iv(index, kappa * a) * numpy.sqrt(pi / (2 * kappa * a))
i1p = -numpy.sqrt(pi / 2) * 1 / (2 * (kappa * a)**(3 / 2.)) * special.iv(
index, kappa * a) + numpy.sqrt(pi / (2 * kappa * a)) * I1p
B = numpy.zeros((N, N), dtype=float)
for n in range(N):
for m in range(N):
for nu in range(N):
if n >= nu and m >= nu:
g1 = gamma(n - nu + 0.5)
g2 = gamma(m - nu + 0.5)
g3 = gamma(nu + 0.5)
g4 = gamma(m + n - nu + 1.5)
f1 = factorial(n + m - nu)
f2 = factorial(n - nu)
f3 = factorial(m - nu)
f4 = factorial(nu)
Anm = g1 * g2 * g3 * f1 * (n + m - 2 * nu + 0.5) / (
pi * g4 * f2 * f3 * f4)
kB = special.kv(n + m - 2 * nu + 0.5, kappa *
R) * numpy.sqrt(pi / (2 * kappa * R))
B[n, m] += Anm * kB
M = numpy.zeros((N, N), float)
for i in range(N):
for j in range(N):
M[i, j] = (2 * i + 1) * B[i, j] * (
E_p / epsilon * i * i1[i] - a * kappa * i1p[i])
if i == j:
M[i, j] += (E_p / epsilon * i * k1[i] - a * kappa * k1p[i])
RHS = numpy.zeros(N)
RHS[0] = a * sigma / epsilon
a_coeff = linalg.solve(M, RHS)
a0 = a_coeff[0]
C0 = a * sigma / epsilon
CC0 = qe**2 * Na * 1e-3 * 1e10 / (cal2J * E_0)
E_inter = 4 * pi * a * epsilon * C0 * C0 * CC0(pi * a0 / (2 * C0 * (
kappa * a * numpy.cosh(kappa * a) - numpy.sinh(kappa * a))) - 1 / (
1 + kappa * a) - 1 / (kappa * a * 1 / numpy.tanh(kappa * a) - 1))
return E_inter
[docs]def Cext_analytical(radius, wavelength, diel_out, diel_in):
"""
Calculates the analytical solution of the extinction cross section.
This solution is valid when the nano particle involved is a sphere.
Arguments
----------
radius : float, radius of the sphere in [nm].
wavelength: float/array of floats, wavelength of the incident
electric field in [nm].
diel_out : complex/array of complex, dielectric constant inside surface.
diel_in : complex/array of complex, dielectric constant inside surface.
Returns
--------
Cext_an : float/array of floats, extinction cross section.
"""
wavenumber = 2 * numpy.pi * numpy.sqrt(diel_out) / wavelength
C1 = wavenumber**2 * (diel_in / diel_out - 1) / (diel_in / diel_out + 2)
Cext_an = 4 * numpy.pi * radius**3 / wavenumber.real * C1.imag
return Cext_an
