ParticleBConds.h

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//////////////////////////////////////////////////////////////////////////////////////
// This file is distributed under the University of Illinois/NCSA Open Source License.
// See LICENSE file in top directory for details.
//
// Copyright (c) 2016 Jeongnim Kim and QMCPACK developers.
//
// File developed by: Jeremy McMinnis, jmcminis@gmail.com, University of Illinois at Urbana-Champaign
//                    Jeongnim Kim, jeongnim.kim@gmail.com, University of Illinois at Urbana-Champaign
//
// File created by: Jeongnim Kim, jeongnim.kim@gmail.com, University of Illinois at Urbana-Champaign
//////////////////////////////////////////////////////////////////////////////////////


#ifndef QMCPLUSPLUS_PARTICLE_BCONDS_H
#define QMCPLUSPLUS_PARTICLE_BCONDS_H

#include <config.h>
#include "CPU/SIMD/vmath.hpp"
#include "Lattice/CrystalLattice.h"

namespace qmcplusplus
{
template<int N, unsigned D>
struct PowerOfN
{
  enum
  {
    value = N * PowerOfN<N, D - 1>::value
  };
};

template<int N>
struct PowerOfN<N, 0>
{
  enum
  {
    value = 1
  };
};

/** @defgroup BoundaryHandlers Templates to handle boundary conditions
 *  @brief generic Boundary condition handler
 *
 * @tparam T real data type
 * @tparam D physical dimension
 * @tparam SC supercell type
 *
 * Default method for any dimension with OPEN boundary condition.
 * \htmlonly
 <table>
 <th>
 <td>SC</td><td>3D</td><td>2D</td><td>1D</td><td>comment</td>
 </th>
 <tr><td>SUPERCELL_OPEN           </td><td>n n n</td><td>n n</td><td>n</td><td>open boudary conditions </td> </tr>
 <tr><td>SUPERCELL_BULK           </td><td>p p p</td><td>NA   </td><td>NA</td><td>periodic boundary conditions in 3 dimensions, general cell</td> </tr>
 <tr><td>SUPERCELL_BULK+TwoPowerD </td><td>p p p</td><td>NA   </td><td>NA</td><td>periodic boundary conditions in 3 dimensions, orthorombic cell</td></tr>
 <tr><td>SUPERCELL_SLAB           </td><td>p p n</td><td>p p</td><td>NA</td><td>periodic boundary conditions in 2 dimensions, general cell</td></tr>
 <tr><td>SUPERCELL_SLAB+TwoPowerD </td><td>p p n</td><td>p p</td><td>NA</td><td>periodic boundary conditions in 2 dimensions, orthorombic cell</td></tr>
 <tr><td>SUPERCELL_WIRE           </td><td>p n n</td><td>p n</td><td>p</td><td>periodic boundary conditions in 1 dimension</td></tr>
 </table>
 * \endhtmlonly
 * Specialization of DTD_BConds should implement
 * - apply_bc(TinyVector<T,D>& displ): apply BC on displ, Cartesian displacement vector, and returns |displ|^2
 * - apply_bc(dr,r,rinv): apply BC on displacements
 * - apply_bc(dr,r): apply BC without inversion calculations
 * - evaluate_rsq(dr,rr,n): apply BC on dr, and compute r*r
 */
template<class T, unsigned D, int SC>
struct DTD_BConds
{
  /** constructor: doing nothing */
  inline DTD_BConds(const CrystalLattice<T, D>& lat) {}

  /** apply BC on displ and return |displ|^2
   * @param displ a displacement vector in the Cartesian coordinate
   * @return \f$|displ|^2\f$
   */
  inline T apply_bc(TinyVector<T, D>& displ) const { return dot(displ, displ); }

  /** apply BC on dr and evaluate r and rinv
   * @param dr vector of displacements, in and out
   * @param r vector of distances
   * @param rinv vector of 1/r
   *
   * The input displacement vectors are not modified with the open boundary conditions.
   */
  inline void apply_bc(std::vector<TinyVector<T, D>>& dr, std::vector<T>& r, std::vector<T>& rinv) const
  {
    const int n = dr.size();
    for (int i = 0; i < n; ++i)
      rinv[i] = dot(dr[i], dr[i]);
    simd::sqrt(&rinv[0], &r[0], n);
    simd::inv(&r[0], &rinv[0], n);
  }

  inline void apply_bc(std::vector<TinyVector<T, D>>& dr, std::vector<T>& r) const
  {
    for (int i = 0; i < dr.size(); ++i)
      r[i] = std::sqrt(dot(dr[i], dr[i]));
  }

  inline void evaluate_rsquared(TinyVector<T, D>* restrict dr, T* restrict rr, int n)
  {
    for (int i = 0; i < n; ++i)
      rr[i] = dot(dr[i], dr[i]);
  }
};

} // namespace qmcplusplus

#if OHMMS_DIM == 3
#include "Lattice/ParticleBConds3D.h"
#elif OHMMS_DIM == 2
#include "Lattice/ParticleBConds2D.h"
#endif

#endif // OHMMS_PARTICLE_BCONDS_H