DrudeLangevinIntegrator

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//
// Title:       Force Field X.
// Description: Force Field X - Software for Molecular Biophysics.
// Copyright:   Copyright (c) Michael J. Schnieders 2001-2025.
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package ffx.openmm.drude;

import static edu.uiowa.jopenmm.OpenMMDrudeLibrary.OpenMM_DrudeLangevinIntegrator_computeDrudeTemperature;
import static edu.uiowa.jopenmm.OpenMMDrudeLibrary.OpenMM_DrudeLangevinIntegrator_computeSystemTemperature;
import static edu.uiowa.jopenmm.OpenMMDrudeLibrary.OpenMM_DrudeLangevinIntegrator_create;
import static edu.uiowa.jopenmm.OpenMMDrudeLibrary.OpenMM_DrudeLangevinIntegrator_destroy;
import static edu.uiowa.jopenmm.OpenMMDrudeLibrary.OpenMM_DrudeLangevinIntegrator_getDrudeFriction;
import static edu.uiowa.jopenmm.OpenMMDrudeLibrary.OpenMM_DrudeLangevinIntegrator_getFriction;
import static edu.uiowa.jopenmm.OpenMMDrudeLibrary.OpenMM_DrudeLangevinIntegrator_getTemperature;
import static edu.uiowa.jopenmm.OpenMMDrudeLibrary.OpenMM_DrudeLangevinIntegrator_setDrudeFriction;
import static edu.uiowa.jopenmm.OpenMMDrudeLibrary.OpenMM_DrudeLangevinIntegrator_setFriction;
import static edu.uiowa.jopenmm.OpenMMDrudeLibrary.OpenMM_DrudeLangevinIntegrator_setTemperature;
import static edu.uiowa.jopenmm.OpenMMDrudeLibrary.OpenMM_DrudeLangevinIntegrator_step;

/**
 * This Integrator simulates systems that include Drude particles.  It applies two different Langevin
 * thermostats to different parts of the system.  The first is applied to ordinary particles (ones that
 * are not part of a Drude particle pair), as well as to the center of mass of each Drude particle pair.
 * A second thermostat, typically with a much lower temperature, is applied to the relative internal
 * displacement of each pair.
 * <p>
 * This integrator can optionally set an upper limit on how far any Drude particle is ever allowed to
 * get from its parent particle.  This can sometimes help to improve stability.  The limit is enforced
 * with a hard wall constraint.  By default the limit is set to 0.02 nm.
 * <p>
 * This Integrator requires the System to include a DrudeForce, which it uses to identify the Drude
 * particles.
 */
public class DrudeLangevinIntegrator extends DrudeIntegrator {

  /**
   * Create a DrudeLangevinIntegrator.
   *
   * @param stepSize         the step size with which to integrator the system (in picoseconds)
   * @param temperature      the temperature of the main heat bath (in Kelvin)
   * @param friction         the friction coefficient which couples the system to the main heat bath (in inverse picoseconds)
   * @param drudeTemperature the temperature of the heat bath applied to internal coordinates of Drude particles (in Kelvin)
   * @param drudeFriction    the friction coefficient which couples the system to the heat bath applied to internal coordinates of Drude particles (in inverse picoseconds)
   */
  public DrudeLangevinIntegrator(double stepSize, double temperature, double friction,
                                 double drudeTemperature, double drudeFriction) {
    super(OpenMM_DrudeLangevinIntegrator_create(stepSize, temperature, friction,
        drudeTemperature, drudeFriction));
  }

  /**
   * Compute the instantaneous temperature of the Drude system, measured in Kelvin.
   * This is calculated based on the kinetic energy of the internal motion of Drude pairs
   * and should remain close to the prescribed Drude temperature.
   */
  public double computeDrudeTemperature() {
    return OpenMM_DrudeLangevinIntegrator_computeDrudeTemperature(pointer);
  }

  /**
   * Compute the instantaneous temperature of the System, measured in Kelvin.
   * This is calculated based on the kinetic energy of the ordinary particles (ones
   * not attached to a Drude particle), as well as the center of mass motion of the
   * Drude particle pairs.  It does not include the internal motion of the pairs.
   * On average, this should be approximately equal to the value returned by
   * getTemperature().
   */
  public double computeSystemTemperature() {
    return OpenMM_DrudeLangevinIntegrator_computeSystemTemperature(pointer);
  }

  /**
   * Destroy the integrator.
   * <p>
   * This method releases the memory associated with the DrudeLangevinIntegrator object.
   * After calling this method, the integrator should not be used.
   */
  @Override
  public void destroy() {
    if (pointer != null) {
      OpenMM_DrudeLangevinIntegrator_destroy(pointer);
      pointer = null;
    }
  }

  /**
   * Get the friction coefficient which determines how strongly the internal coordinates of Drude particles
   * are coupled to the heat bath (in inverse ps).
   *
   * @return the friction coefficient, measured in 1/ps
   */
  public double getDrudeFriction() {
    return OpenMM_DrudeLangevinIntegrator_getDrudeFriction(pointer);
  }

  /**
   * Get the friction coefficient which determines how strongly the system is coupled to
   * the main heat bath (in inverse ps).
   *
   * @return the friction coefficient, measured in 1/ps
   */
  public double getFriction() {
    return OpenMM_DrudeLangevinIntegrator_getFriction(pointer);
  }

  /**
   * Get the temperature of the main heat bath (in Kelvin).
   *
   * @return the temperature of the heat bath, measured in Kelvin
   */
  public double getTemperature() {
    return OpenMM_DrudeLangevinIntegrator_getTemperature(pointer);
  }

  /**
   * Set the friction coefficient which determines how strongly the internal coordinates of Drude particles
   * are coupled to the heat bath (in inverse ps).
   *
   * @param friction the friction coefficient, measured in 1/ps
   */
  public void setDrudeFriction(double friction) {
    OpenMM_DrudeLangevinIntegrator_setDrudeFriction(pointer, friction);
  }

  /**
   * Set the friction coefficient which determines how strongly the system is coupled to
   * the main heat bath (in inverse ps).
   *
   * @param friction the friction coefficient, measured in 1/ps
   */
  public void setFriction(double friction) {
    OpenMM_DrudeLangevinIntegrator_setFriction(pointer, friction);
  }

  /**
   * Set the temperature of the main heat bath (in Kelvin).
   *
   * @param temperature the temperature of the heat bath, measured in Kelvin
   */
  public void setTemperature(double temperature) {
    OpenMM_DrudeLangevinIntegrator_setTemperature(pointer, temperature);
  }

  /**
   * Advance a simulation through time by taking a series of time steps.
   *
   * @param steps the number of time steps to take
   */
  @Override
  public void step(int steps) {
    OpenMM_DrudeLangevinIntegrator_step(pointer, steps);
  }
}