EwaldHandlerQuasi2D.cpp

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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) 2022 QMCPACK developers.
//
// File developed by: Jeongnim Kim, jeongnim.kim@gmail.com, University of Illinois at Urbana-Champaign
//                    Jeremy McMinnis, jmcminis@gmail.com, University of Illinois at Urbana-Champaign
//                    Mark A. Berrill, berrillma@ornl.gov, Oak Ridge National Laboratory
//                    Yubo "Paul" Yang, yubo.paul.yang@gmail.com, CCQ @ Flatiron
//
// File created by: Jeongnim Kim, jeongnim.kim@gmail.com, University of Illinois at Urbana-Champaign
//////////////////////////////////////////////////////////////////////////////////////

#include "Particle/LongRange/EwaldHandlerQuasi2D.h"

namespace qmcplusplus
{

EwaldHandlerQuasi2D::EwaldHandlerQuasi2D(ParticleSet& ref, mRealType kc_in)
  : LRHandlerBase(kc_in)
{
  if (ref.getLattice().SuperCellEnum != SUPERCELL_SLAB)
    throw std::runtime_error("Quasi2D Ewald requires ppn boundary.");
  LR_rc = ref.getLattice().LR_rc; // CoulombPBC needs get_rc() to createSpline4RbyVs
  LR_kc = ref.getLattice().LR_kc; // get_kc() is used in QMCFiniteSize
  alpha = std::sqrt(LR_kc/2.0/LR_rc);
  area = ref.getLattice().Volume/ref.getLattice().R(2,2);
  // report
  app_log() << "    alpha = " << alpha << " area = " << area << std::endl;
  fillFk(ref.getSimulationCell().getKLists());
}

void EwaldHandlerQuasi2D::fillFk(const KContainer& KList)
{
  const mRealType knorm = M_PI / area;
  mRealType kmag, uk;

  Fk.resize(KList.kpts_cart.size());
  MaxKshell = KList.kshell.size() - 1;
  Fk_symm.resize(MaxKshell);

  kmags.resize(MaxKshell);
  for (int ks = 0, ki = 0; ks < Fk_symm.size(); ks++)
  {
    kmag = std::sqrt(KList.ksq[ki]);
    kmags[ks] = kmag; // store k magnitutes
    uk = knorm/kmag;
    Fk_symm[ks] = uk;
    while (ki < KList.kshell[ks + 1] && ki < Fk.size())
      Fk[ki++] = uk;
  }
}

EwaldHandlerQuasi2D::mRealType EwaldHandlerQuasi2D::evaluate_slab(
  pRealType z, const std::vector<int>& kshell,
  const pRealType* restrict rk1_r,
  const pRealType* restrict rk1_i,
  const pRealType* restrict rk2_r,
  const pRealType* restrict rk2_i) const
{
  mRealType zmag = std::abs(z);
  mRealType vk = -slab_vsr_k0(zmag)/area;
  for (int ks = 0, ki = 0; ks < MaxKshell; ks++)
  {
    mRealType u = 0;
    for (; ki < kshell[ks + 1]; ki++)
      u += (*rk1_r++) * (*rk2_r++) + (*rk1_i++) * (*rk2_i++);
    vk += u * Fk_symm[ks] * slabFunc(zmag, kmags[ks]);
  }
  return vk;
}

EwaldHandlerQuasi2D::mRealType EwaldHandlerQuasi2D::slabFunc(mRealType z, mRealType k) const
{
  mRealType term1, term2;
  term1 = std::exp(slabLogf( z, k));
  term2 = std::exp(slabLogf(-z, k));
  return term1+term2;
}

EwaldHandlerQuasi2D::mRealType EwaldHandlerQuasi2D::slabLogf(mRealType z, mRealType k) const
{
  mRealType z1 = alpha*z;
  mRealType k1 = k/(2*alpha);
  mRealType log_term = k*z + std::log(erfc(z1+k1));
  return log_term;
}

EwaldHandlerQuasi2D::mRealType EwaldHandlerQuasi2D::slab_vsr_k0(mRealType z) const
{
  mRealType z1 = alpha*z;
  mRealType term1 = std::exp(-z1*z1) * 2*std::sqrt(M_PI)/alpha;
  mRealType term2 = 2*M_PI*z*erfc(z1);
  return term1-term2;
}

} // qmcplusplus