ComputeNonbondedAlch.h File Reference

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Functions
void	vdw_forceandenergy (const BigReal A, const BigReal B, const BigReal r2, BigReal *U, BigReal *F)
void	vdw_energy (const BigReal A, const BigReal B, const BigReal r2, BigReal *U)
void	vdw_switch (const BigReal r2, const BigReal switchdist2, const BigReal cutoff2, const BigReal switchfactor, BigReal *switchmul, BigReal *switchmul2)
void	vdw_fswitch_forceandenergy (const BigReal A, const BigReal B, const BigReal r2, const BigReal switchdist2, const BigReal cutoff2, BigReal *U, BigReal *F)
void	vdw_fswitch_energy (const BigReal A, const BigReal B, const BigReal r2, const BigReal switchdist2, const BigReal cutoff2, BigReal *U)
void	vdw_fswitch_shift (const BigReal A, const BigReal B, const BigReal switchdist2, const BigReal cutoff2, BigReal *dU)

Function Documentation

vdw_energy()

void vdw_energy ( const BigReal  A, const BigReal  B, const BigReal  r2, BigReal *  U  )

inline

Definition at line 25 of file ComputeNonbondedAlch.h.

Referenced by fep_vdw_forceandenergies().

                                  {
  const BigReal inv_r2 = 1. / r2;
  const BigReal inv_r6 = inv_r2*inv_r2*inv_r2;
  *U = inv_r6*(A*inv_r6 - B);
}

vdw_forceandenergy()

void vdw_forceandenergy ( const BigReal  A, const BigReal  B, const BigReal  r2, BigReal *  U, BigReal *  F  )

inline

Copyright (c) 1995, 1996, 1997, 1998, 1999, 2000 by The Board of Trustees of the University of Illinois. All rights reserved.

Definition at line 16 of file ComputeNonbondedAlch.h.

Referenced by fep_vdw_forceandenergies(), and ti_vdw_force_energy_dUdl().

                                              {
  const BigReal inv_r2 = 1. / r2;
  const BigReal inv_r6 = inv_r2*inv_r2*inv_r2;
  *U = inv_r6*(A*inv_r6 - B);
  *F = 6*inv_r2*(2*(*U) + B*inv_r6);
}

vdw_fswitch_energy()

void vdw_fswitch_energy ( const BigReal  A, const BigReal  B, const BigReal  r2, const BigReal  switchdist2, const BigReal  cutoff2, BigReal *  U  )

inline

Definition at line 75 of file ComputeNonbondedAlch.h.

Referenced by fep_vdw_forceandenergies().

                {  
  // TODO: Some rearrangement could be done to use rsqrt() instead?
  const BigReal inv_r2 = 1. / r2;
  const BigReal inv_r6 = inv_r2*inv_r2*inv_r2;
  const BigReal inv_r3 = sqrt(inv_r6);
  const BigReal inv_cutoff6 = 1. / (cutoff2*cutoff2*cutoff2);
  const BigReal inv_cutoff3 = sqrt(inv_cutoff6);
  const BigReal switchdist6 = switchdist2*switchdist2*switchdist2;
  const BigReal k_vdwa = A / (1 - switchdist6*inv_cutoff6);
  const BigReal k_vdwb = B / (1 - sqrt(switchdist6*inv_cutoff6));
  const BigReal tmpa = inv_r6 - inv_cutoff6;
  const BigReal tmpb = inv_r3 - inv_cutoff3;
  *U = k_vdwa*tmpa*tmpa - k_vdwb*tmpb*tmpb;
}

vdw_fswitch_forceandenergy()

void vdw_fswitch_forceandenergy ( const BigReal  A, const BigReal  B, const BigReal  r2, const BigReal  switchdist2, const BigReal  cutoff2, BigReal *  U, BigReal *  F  )

inline

Definition at line 56 of file ComputeNonbondedAlch.h.

Referenced by fep_vdw_forceandenergies(), and ti_vdw_force_energy_dUdl().

                            {
  // TODO: Some rearrangement could be done to use rsqrt() instead?
  const BigReal inv_r2 = 1. / r2;
  const BigReal inv_r6 = inv_r2*inv_r2*inv_r2;
  const BigReal inv_r3 = sqrt(inv_r6);
  const BigReal inv_cutoff6 = 1. / (cutoff2*cutoff2*cutoff2);
  const BigReal inv_cutoff3 = sqrt(inv_cutoff6);
  const BigReal switchdist6 = switchdist2*switchdist2*switchdist2;
  const BigReal k_vdwa = A / (1 - switchdist6*inv_cutoff6);
  const BigReal k_vdwb = B / (1 - sqrt(switchdist6*inv_cutoff6));
  const BigReal tmpa = inv_r6 - inv_cutoff6;
  const BigReal tmpb = inv_r3 - inv_cutoff3;
  *U = k_vdwa*tmpa*tmpa - k_vdwb*tmpb*tmpb;
  *F = 6*inv_r2*(2*k_vdwa*tmpa*inv_r6 - k_vdwb*tmpb*inv_r3);
}

vdw_fswitch_shift()

void vdw_fswitch_shift ( const BigReal  A, const BigReal  B, const BigReal  switchdist2, const BigReal  cutoff2, BigReal *  dU  )

inline

Definition at line 97 of file ComputeNonbondedAlch.h.

Referenced by fep_vdw_forceandenergies(), and ti_vdw_force_energy_dUdl().

                                                                   {
  // TODO: Some rearrangement could be done to use rsqrt() instead.
  const BigReal cutoff6 = cutoff2*cutoff2*cutoff2;
  const BigReal switchdist6 = switchdist2*switchdist2*switchdist2;
  const BigReal v_vdwa = -A / (cutoff6*switchdist6);
  const BigReal v_vdwb = -B / sqrt(cutoff6*switchdist6);
  *dU = v_vdwa - v_vdwb; //deltaV2 from Steinbach & Brooks
}

vdw_switch()

void vdw_switch ( const BigReal  r2, const BigReal  switchdist2, const BigReal  cutoff2, const BigReal  switchfactor, BigReal *  switchmul, BigReal *  switchmul2  )

inline

Definition at line 35 of file ComputeNonbondedAlch.h.

Referenced by fep_vdw_forceandenergies(), and ti_vdw_force_energy_dUdl().

                         {
  if (r2 <= switchdist2) {
    // "switching off" will always fall through here.
    *switchmul = 1.0;
    *switchmul2 = 0.0;
  } else {
    const BigReal cdiff2 = (cutoff2 - r2);
    const BigReal sdiff2 = (r2 - switchdist2);
    *switchmul = switchfactor*cdiff2*cdiff2*(cdiff2 + 3*sdiff2);
    *switchmul2 = 12*switchfactor*cdiff2*sdiff2;
  }
}