1 // ******************************************************************************
2 //
3 // Title: Force Field X.
4 // Description: Force Field X - Software for Molecular Biophysics.
5 // Copyright: Copyright (c) Michael J. Schnieders 2001-2025.
6 //
7 // This file is part of Force Field X.
8 //
9 // Force Field X is free software; you can redistribute it and/or modify it
10 // under the terms of the GNU General Public License version 3 as published by
11 // the Free Software Foundation.
12 //
13 // Force Field X is distributed in the hope that it will be useful, but WITHOUT
14 // ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
15 // FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
16 // details.
17 //
18 // You should have received a copy of the GNU General Public License along with
19 // Force Field X; if not, write to the Free Software Foundation, Inc., 59 Temple
20 // Place, Suite 330, Boston, MA 02111-1307 USA
21 //
22 // Linking this library statically or dynamically with other modules is making a
23 // combined work based on this library. Thus, the terms and conditions of the
24 // GNU General Public License cover the whole combination.
25 //
26 // As a special exception, the copyright holders of this library give you
27 // permission to link this library with independent modules to produce an
28 // executable, regardless of the license terms of these independent modules, and
29 // to copy and distribute the resulting executable under terms of your choice,
30 // provided that you also meet, for each linked independent module, the terms
31 // and conditions of the license of that module. An independent module is a
32 // module which is not derived from or based on this library. If you modify this
33 // library, you may extend this exception to your version of the library, but
34 // you are not obligated to do so. If you do not wish to do so, delete this
35 // exception statement from your version.
36 //
37 // ******************************************************************************
38 package ffx.openmm;
39
40 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_LangevinMiddleIntegrator_create;
41 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_LangevinMiddleIntegrator_destroy;
42 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_LangevinMiddleIntegrator_getFriction;
43 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_LangevinMiddleIntegrator_getRandomNumberSeed;
44 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_LangevinMiddleIntegrator_getTemperature;
45 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_LangevinMiddleIntegrator_setFriction;
46 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_LangevinMiddleIntegrator_setRandomNumberSeed;
47 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_LangevinMiddleIntegrator_setTemperature;
48 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_LangevinMiddleIntegrator_step;
49
50 /**
51 * This is an Integrator which simulates a System using Langevin dynamics, with
52 * the LFMiddle discretization (J. Phys. Chem. A 2019, 123, 28, 6056-6079).
53 * This method tend to produce more accurate configurational sampling than other
54 * discretizations, such as the one used in LangevinIntegrator.
55 * <p>
56 * The algorithm is closely related to the BAOAB discretization
57 * (Proc. R. Soc. A. 472: 20160138). Both methods produce identical trajectories,
58 * but LFMiddle returns half step (leapfrog) velocities, while BAOAB returns
59 * on-step velocities. The former provide a much more accurate sampling of the
60 * thermal ensemble.
61 */
62 public class LangevinMiddleIntegrator extends Integrator {
63
64 /**
65 * Create a LangevinMiddleIntegrator.
66 *
67 * @param dt the step size with which to integrate the system (in picoseconds)
68 * @param temp the temperature of the heat bath (in Kelvin)
69 * @param gamma the friction coefficient which couples the system to the heat bath (in inverse picoseconds)
70 */
71 public LangevinMiddleIntegrator(double dt, double temp, double gamma) {
72 super(OpenMM_LangevinMiddleIntegrator_create(temp, gamma, dt));
73 }
74
75 /**
76 * Destroy the integrator.
77 */
78 @Override
79 public void destroy() {
80 if (pointer != null) {
81 OpenMM_LangevinMiddleIntegrator_destroy(pointer);
82 pointer = null;
83 }
84 }
85
86 /**
87 * Get the friction coefficient.
88 *
89 * @return The friction coefficient in inverse picoseconds.
90 */
91 public double getFriction() {
92 return OpenMM_LangevinMiddleIntegrator_getFriction(pointer);
93 }
94
95 /**
96 * Get the random number seed.
97 *
98 * @return The random number seed.
99 */
100 public int getRandomNumberSeed() {
101 return OpenMM_LangevinMiddleIntegrator_getRandomNumberSeed(pointer);
102 }
103
104 /**
105 * Get the temperature.
106 *
107 * @return The temperature in Kelvin.
108 */
109 public double getTemperature() {
110 return OpenMM_LangevinMiddleIntegrator_getTemperature(pointer);
111 }
112
113 /**
114 * Set the friction coefficient.
115 *
116 * @param gamma The friction coefficient in inverse picoseconds.
117 */
118 public void setFriction(double gamma) {
119 OpenMM_LangevinMiddleIntegrator_setFriction(pointer, gamma);
120 }
121
122 /**
123 * Set the random number seed.
124 *
125 * @param seed The random number seed.
126 */
127 public void setRandomNumberSeed(int seed) {
128 OpenMM_LangevinMiddleIntegrator_setRandomNumberSeed(pointer, seed);
129 }
130
131 /**
132 * Set the temperature.
133 *
134 * @param temp The temperature in Kelvin.
135 */
136 public void setTemperature(double temp) {
137 OpenMM_LangevinMiddleIntegrator_setTemperature(pointer, temp);
138 }
139
140 /**
141 * Step the integrator.
142 *
143 * @param steps The number of steps to take.
144 */
145 @Override
146 public void step(int steps) {
147 OpenMM_LangevinMiddleIntegrator_step(pointer, steps);
148 }
149 }