SwitchingFunction.cpp

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 *
 * SUPPORT OPEN SCIENCE!  If you use OpenMD or its source code in your
 * research, please cite the following paper when you publish your work:
 *
 * [1] Drisko et al., J. Open Source Softw. 9, 7004 (2024).
 *
 * Good starting points for code and simulation methodology are:
 *
 * [2] Meineke, et al., J. Comp. Chem. 26, 252-271 (2005).
 * [3] Fennell & Gezelter, J. Chem. Phys. 124, 234104 (2006).
 * [4] Sun, Lin & Gezelter, J. Chem. Phys. 128, 234107 (2008).
 * [5] Vardeman, Stocker & Gezelter, J. Chem. Theory Comput. 7, 834 (2011).
 * [6] Kuang & Gezelter, Mol. Phys., 110, 691-701 (2012).
 * [7] Lamichhane, Gezelter & Newman, J. Chem. Phys. 141, 134109 (2014).
 * [8] Bhattarai, Newman & Gezelter, Phys. Rev. B 99, 094106 (2019).
 * [9] Drisko & Gezelter, J. Chem. Theory Comput. 20, 4986-4997 (2024).
 */
 
#include "nonbonded/SwitchingFunction.hpp"
 
#include <cmath>
#include <cstdio>
#include <iostream>
 
#include "utils/simError.h"
 
using namespace std;
namespace OpenMD {
 
  SwitchingFunction::SwitchingFunction() :
      functionType_(cubic), haveSpline_(false), isCubic_(true), np_(150) {
    switchSpline_ = std::make_shared<CubicSpline>();
  }
 
  void SwitchingFunction::setSwitchType(SwitchingFunctionType sft) {
    if ((sft == fifth_order_poly) || (sft == cubic)) {
      if (haveSpline_) {
        switchSpline_ = std::make_shared<CubicSpline>();
        setSwitch(rin_, rout_);
      }
    } else {
      snprintf(
          painCave.errMsg, MAX_SIM_ERROR_MSG_LENGTH,
          "SwitchingFunction::setSwitchType was given unknown function type\n");
      painCave.severity = OPENMD_ERROR;
      painCave.isFatal  = 1;
      simError();
    }
  }
 
  void SwitchingFunction::setSwitch(RealType rinner, RealType router) {
    if (router < rinner) {
      snprintf(painCave.errMsg, MAX_SIM_ERROR_MSG_LENGTH,
               "SwitchingFunction::setSwitch was given rinner (%lf) which was\n"
               "\tlarger than router (%lf).\n",
               rinner, router);
      painCave.severity = OPENMD_ERROR;
      painCave.isFatal  = 1;
      simError();
    }
    if (router < 0.0) {
      snprintf(painCave.errMsg, MAX_SIM_ERROR_MSG_LENGTH,
               "SwitchingFunction::setSwitch was given router (%lf) which was\n"
               "\tless than zero.\n",
               router);
      painCave.severity = OPENMD_ERROR;
      painCave.isFatal  = 1;
      simError();
    }
    if (rinner < 0.0) {
      snprintf(painCave.errMsg, MAX_SIM_ERROR_MSG_LENGTH,
               "SwitchingFunction::setSwitch was given rinner (%lf) which was\n"
               "\tless than zero.\n",
               router);
      painCave.severity = OPENMD_ERROR;
      painCave.isFatal  = 1;
      simError();
    }
 
    rin_   = rinner;
    rout_  = router;
    rin2_  = rin_ * rin_;
    rout2_ = rout_ * rout_;
 
    if ((router - rinner) < 1.0e-8) {
      // no reason to set up spline if the switching region is tiny
      return;
    }
 
    // setup r -> sw lookup spline
    if (functionType_ == fifth_order_poly) {
      isCubic_    = false;
      RealType c0 = 1.0;
      RealType c3 = -10.0;
      RealType c4 = 15.0;
      RealType c5 = -6.0;
 
      RealType dx, r, yval, rval, rval2, rval3, rval4, rval5;
      RealType rvaldi, rvaldi2, rvaldi3, rvaldi4, rvaldi5;
 
      dx = (rout_ - rin_) / RealType(np_ - 1);
 
      for (int i = 0; i < np_; i++) {
        r       = rin_ + RealType(i) * dx;
        rval    = (r - rin_);
        rval2   = rval * rval;
        rval3   = rval2 * rval;
        rval4   = rval2 * rval2;
        rval5   = rval3 * rval2;
        rvaldi  = 1.0 / (rout_ - rin_);
        rvaldi2 = rvaldi * rvaldi;
        rvaldi3 = rvaldi2 * rvaldi;
        rvaldi4 = rvaldi2 * rvaldi2;
        rvaldi5 = rvaldi3 * rvaldi2;
        yval    = c0 + c3 * rval3 * rvaldi3 + c4 * rval4 * rvaldi4 +
               c5 * rval5 * rvaldi5;
        switchSpline_->addPoint(r, yval);
      }
    } else {
      // cubic splines only need 2 points to do a cubic switching function...
      isCubic_ = true;
      switchSpline_->addPoint(rin_, 1.0);
      switchSpline_->addPoint(rout_, 0.0);
    }
    haveSpline_ = true;
    return;
  }
 
  bool SwitchingFunction::getSwitch(const RealType& r2, RealType& sw,
                                    RealType& dswdr, RealType& r) {
    sw    = 1.0;
    dswdr = 0.0;
 
    bool in_switching_region = false;
 
    if (r2 > rin2_) {
      if (r2 > rout2_) {
        sw = 0.0;
      } else {
        in_switching_region = true;
        r                   = sqrt(r2);
        switchSpline_->getValueAndDerivativeAt(r, sw, dswdr);
      }
    }
    return in_switching_region;
  }
}  // namespace OpenMD