Velocitizer.hpp

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 * SUPPORT OPEN SCIENCE!  If you use OpenMD or its source code in your
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 * work.  Good starting points are:
 *
 * [1] Meineke, et al., J. Comp. Chem. 26, 252-271 (2005).
 * [2] Fennell & Gezelter, J. Chem. Phys. 124, 234104 (2006).
 * [3] Sun, Lin & Gezelter, J. Chem. Phys. 128, 234107 (2008).
 * [4] Vardeman, Stocker & Gezelter, J. Chem. Theory Comput. 7, 834 (2011).
 * [5] Kuang & Gezelter, Mol. Phys., 110, 691-701 (2012).
 * [6] Lamichhane, Gezelter & Newman, J. Chem. Phys. 141, 134109 (2014).
 * [7] Lamichhane, Newman & Gezelter, J. Chem. Phys. 141, 134110 (2014).
 * [8] Bhattarai, Newman & Gezelter, Phys. Rev. B 99, 094106 (2019).
 */
 
#ifndef BRAINS_VELOCITIZER_HPP
#define BRAINS_VELOCITIZER_HPP
 
#include "brains/SimInfo.hpp"
#include "brains/Thermo.hpp"
#include "io/Globals.hpp"
#include "utils/RandNumGen.hpp"
 
namespace OpenMD {
 
  //! Velocity-modifying routines.
  /*
    Provides functions that re-sample or re-scale the velocities.
    These are particularly useful for setting initial configurations
    to a desired temperature or re-scaling velocities to match a
    desired energy.
  */
  class Velocitizer {
  public:
    Velocitizer(SimInfo* info);
    virtual ~Velocitizer() = default;
 
    /** @brief Resamples velocities and angular momenta
     * Resamples velocities and angular momenta from a Maxwell-Boltzmann
     * distribution.
     * @param t : Temperature of the new distribution.
     */
    void randomize(RealType ct);
 
    /** @brief Resamples charge velocities
     * Resamples charge velocities from a Maxwell-Boltzmann
     * distribution.
     * @param ct : Charge temperature of the new distribution.
     */
    void randomizeChargeVelocity(RealType ct);
 
    /** @brief Scales velocities and angular momenta by a scaling factor
     * Rescales velocity (and angular momenta) by a scaling factor.
     * @param lambda : Scaling factor (must be >= 0)
     */
    void scale(RealType lambda);
 
    /** @brief Removes Center of Mass Drift Velocity
     * Removes the center of mass drift velocity (required for accurate
     * calculations of diffusion).
     */
    void removeComDrift();
 
    /** @brief Removes Center of Mass Angular momentum
     * Removes the center of mass angular momentum (particularly useful in
     * non-periodic simulations).
     */
    void removeAngularDrift();
 
  private:
    SimInfo* info_ {nullptr};
    Thermo thermo_;
    Globals* globals_;
    Utils::RandNumGenPtr randNumGen_ {nullptr};
  };
}  // namespace OpenMD
 
#endif  // BRAINS_VELOCITIZER_HPP