ESPResSo
Extensible Simulation Package for Research on Soft Matter Systems
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buckingham.hpp
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1/*
2 * Copyright (C) 2010-2022 The ESPResSo project
3 * Copyright (C) 2002,2003,2004,2005,2006,2007,2008,2009,2010
4 * Max-Planck-Institute for Polymer Research, Theory Group
5 *
6 * This file is part of ESPResSo.
7 *
8 * ESPResSo is free software: you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License as published by
10 * the Free Software Foundation, either version 3 of the License, or
11 * (at your option) any later version.
12 *
13 * ESPResSo is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
17 *
18 * You should have received a copy of the GNU General Public License
19 * along with this program. If not, see <http://www.gnu.org/licenses/>.
20 */
21#ifndef BUCKINGHAM_H
22#define BUCKINGHAM_H
23/** \file
24 * Routines to calculate the Buckingham potential between particle pairs.
25 *
26 * Implementation in \ref buckingham.cpp.
27 */
28
29#include "config/config.hpp"
30
31#ifdef BUCKINGHAM
32
34
35#include <cmath>
36
37/**Resultant Force due to a Buckingham potential between two particles at
38 * interatomic separation r greater than or equal to discont*/
39inline double buck_force_r(double A, double B, double C, double D, double r) {
40 return (A * B * exp(-B * r) - 6.0 * C / pow(r, 7) - 4.0 * D / pow(r, 5));
41}
42
43/**Potential Energy due to a Buckingham potential between two particles at
44 * interatomic separation r greater than or equal to discont*/
45inline double buck_energy_r(double A, double B, double C, double D,
46 double shift, double r) {
47 return (A * exp(-B * r) - C / pow(r, 6) - D / pow(r, 4) + shift);
48}
49
50/** Calculate Buckingham force factor */
51inline double buck_pair_force_factor(IA_parameters const &ia_params,
52 double dist) {
53 if (dist < ia_params.buckingham.cut) {
54 /* case: resulting force/energy greater than discontinuity and
55 less than cutoff (true Buckingham region) */
56 double fac;
57 if (dist > ia_params.buckingham.discont) {
58 fac = buck_force_r(ia_params.buckingham.A, ia_params.buckingham.B,
59 ia_params.buckingham.C, ia_params.buckingham.D, dist) /
60 dist;
61 } else {
62 /* resulting force/energy in the linear region*/
63 fac = -ia_params.buckingham.F2 / dist;
64 }
65 return fac;
66 }
67 return 0.0;
68}
69
70/** Calculate Buckingham energy */
71inline double buck_pair_energy(IA_parameters const &ia_params, double dist) {
72 if (dist < ia_params.buckingham.cut) {
73 /* case: resulting force/energy greater than discont and
74 less than cutoff (true Buckingham region) */
75 if (dist > ia_params.buckingham.discont) {
76 return buck_energy_r(ia_params.buckingham.A, ia_params.buckingham.B,
77 ia_params.buckingham.C, ia_params.buckingham.D,
78 ia_params.buckingham.shift, dist);
79 }
80
81 /* resulting force/energy in the linear region*/
82 return ia_params.buckingham.F1 + ia_params.buckingham.F2 * dist;
83 }
84 return 0.0;
85}
86
87#endif // BUCKINGHAM
88#endif
double buck_pair_force_factor(IA_parameters const &ia_params, double dist)
Calculate Buckingham force factor.
double buck_pair_energy(IA_parameters const &ia_params, double dist)
Calculate Buckingham energy.
double buck_energy_r(double A, double B, double C, double D, double shift, double r)
Potential Energy due to a Buckingham potential between two particles at interatomic separation r grea...
double buck_force_r(double A, double B, double C, double D, double r)
Resultant Force due to a Buckingham potential between two particles at interatomic separation r great...
This file contains the defaults for ESPResSo.
Various procedures concerning interactions between particles.
Parameters for non-bonded interactions.
Buckingham_Parameters buckingham