test_temp.cpp

//////////////////////////////////////////////////////////////////////////////////////
// This file is distributed under the University of Illinois/NCSA Open Source License.
// See LICENSE file in top directory for details.
//
// Copyright (c) 2019 and QMCPACK developers.
//
// File developed by: Yubo "Paul" Yang, yubo.paul.yang@gmail.com, University of Illinois Urbana-Champaign
//
// File created by: Yubo "Paul" Yang, yubo.paul.yang@gmail.com, University of Illinois Urbana-Champaign
//////////////////////////////////////////////////////////////////////////////////////

#include "catch.hpp"

#include "Configuration.h"
#include "Lattice/CrystalLattice.h"
#include "Particle/ParticleSet.h"
#include "LongRange/LRHandlerTemp.h"

namespace qmcplusplus
{
using mRealType = LRHandlerBase::mRealType;

struct EslerCoulomb3D
{ // stripped down version of LRCoulombSingleton::CoulombFunctor for 3D
  double norm;
  inline double operator()(double r, double rinv) const { return rinv; }
  void reset(ParticleSet& ref) { norm = 4.0 * M_PI / ref.getLRBox().Volume; }
  inline double Xk(double k, double rc) const { return -norm / (k * k) * std::cos(k * rc); }
  inline double Fk(double k, double rc) const { return -Xk(k, rc); }
  inline double integrate_r2(double r) const { return 0.5 * r * r; }
  inline double df(double r) const { return 0; }          // ignore derivatives for now
  void reset(ParticleSet& ref, double rs) { reset(ref); } // ignore rs
};

/** evalaute bare Coulomb in 3D using LRHandlerTemp
 */
TEST_CASE("temp3d", "[lrhandler]")
{
  Lattice lattice;
  lattice.BoxBConds     = true;
  lattice.LR_dim_cutoff = 30.;
  lattice.R.diagonal(5.0);
  lattice.reset();
  CHECK(Approx(lattice.Volume) == 125);
  lattice.SetLRCutoffs(lattice.Rv);
  //lattice.printCutoffs(app_log());
  CHECK(Approx(lattice.LR_rc) == 2.5);
  CHECK(Approx(lattice.LR_kc) == 12);

  const SimulationCell simulation_cell(lattice);
  ParticleSet ref(simulation_cell);       // handler needs ref.getSimulationCell().getKLists()
  ref.createSK();
  LRHandlerTemp<EslerCoulomb3D, LPQHIBasis> handler(ref);

  handler.initBreakup(ref);

  app_log() << "handler.MaxKshell is " << handler.MaxKshell << std::endl;
  CHECK(handler.MaxKshell == 78);
  CHECK(Approx(handler.LR_rc) == 2.5);
  CHECK(Approx(handler.LR_kc) == 12);

  mRealType r, dr, rinv;
  mRealType vsr, vlr;
  int nr = 101;
  dr     = 5.0 / nr; // L/[# of grid points]
  for (int ir = 1; ir < nr; ir++)
  {
    r    = ir * dr;
    rinv = 1. / r;
    vsr  = handler.evaluate(r, rinv);
    vlr  = handler.evaluateLR(r);
    // short-range part must vanish after rcut
    if (r > 2.5)
      CHECK(Approx(vsr) == 0.0);
    // sum must recover the Coulomb potential
    CHECK(vsr + vlr == Approx(rinv));
  }
}

} // namespace qmcplusplus