57 lines
1.8 KiB
C++
57 lines
1.8 KiB
C++
/* ----------------------------------------------------------------------
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LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
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https://www.lammps.org/, Sandia National Laboratories
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LAMMPS development team: developers@lammps.org
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Copyright (2003) Sandia Corporation. Under the terms of Contract
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DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
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certain rights in this software. This software is distributed under
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the GNU General Public License.
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See the README file in the top-level LAMMPS directory.
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------------------------------------------------------------------------- */
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/* ----------------------------------------------------------------------
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Contributing authors: Ludwig Ahrens-Iwers (TUHH), Shern Tee (UQ), Robert Meissner (TUHH)
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------------------------------------------------------------------------- */
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#ifndef LMP_ELECTRODE_MATH_H
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#define LMP_ELECTRODE_MATH_H
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#include "ewald_const.h"
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#include "math_const.h"
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#include <cmath>
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namespace LAMMPS_NS {
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using namespace EwaldConst;
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namespace ElectrodeMath {
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static constexpr double ERFCMAX = 5.8; // erfc(ERFCMAX) < machine epsilon(double)
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static double safe_erfc(double x)
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{
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if (x > ERFCMAX) return 0.0;
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double expm2 = exp(-x * x);
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double t = 1.0 / (1.0 + EWALD_P * x);
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return t * (A1 + t * (A2 + t * (A3 + t * (A4 + t * A5)))) * expm2;
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}
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static double safe_derfcr(double x, double &erfc)
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{
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if (x > ERFCMAX) {
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erfc = 0.0;
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return 0.0;
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}
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double x2 = x * x;
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double expm2 = exp(-x2);
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double t = 1.0 / (1.0 + EWALD_P * x);
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erfc = t * (A1 + t * (A2 + t * (A3 + t * (A4 + t * A5)))) * expm2;
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return -erfc - 2.0 * expm2 * x / MathConst::MY_PIS;
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}
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} // namespace ElectrodeMath
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} // namespace LAMMPS_NS
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#endif
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