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fix_nphug.cpp
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Mon, Nov 4, 10:31

fix_nphug.cpp
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/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
http://lammps.sandia.gov, Sandia National Laboratories
Steve Plimpton, sjplimp@sandia.gov
Copyright (2003) Sandia Corporation. Under the terms of Contract
DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
certain rights in this software. This software is distributed under
the GNU General Public License.
See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */
#include "string.h"
#include "stdlib.h"
#include "fix_nphug.h"
#include "modify.h"
#include "error.h"
#include "update.h"
#include "compute.h"
#include "force.h"
#include "domain.h"
#include "group.h"
#include "math.h"
#include "memory.h"
#include "comm.h"
#include "math.h"
using namespace LAMMPS_NS;
enum{ISO,ANISO,TRICLINIC}; // same as fix_nh.cpp
/* ---------------------------------------------------------------------- */
FixNPHug::FixNPHug(LAMMPS *lmp, int narg, char **arg) :
FixNH(lmp, narg, arg)
{
// Prevent masses from being updated every timestep
eta_mass_flag = 0;
omega_mass_flag = 0;
etap_mass_flag = 0;
// extend vector of base-class computes
size_vector += 3;
// turn off deviatoric flag and remove strain energy from vector
deviatoric_flag = 0;
size_vector -= 1;
// use initial state as reference state
v0_set = p0_set = e0_set = 0;
// check pressure settings
if (p_start[0] != p_stop[0] ||
p_start[1] != p_stop[1] ||
p_start[2] != p_stop[2])
error->all("Invalid argument for fix nphug");
// uniaxial = 0 means hydrostatic compression
// uniaxial = 1 means uniaxial compression
// in x, y, or z (idir = 0, 1, or 2)
// isotropic hydrostatic compression
if (pstyle == ISO) {
uniaxial = 0;
// anisotropic compression
} else if (pstyle == ANISO) {
// anisotropic hydrostatic compression
if (p_start[0] == p_start[1] &&
p_start[0] == p_start[2] )
uniaxial = 0;
// uniaxial compression
else if (p_flag[0] == 1 && p_flag[1] == 0
&& p_flag[2] == 0) {
uniaxial = 1;
idir = 0;
} else if (p_flag[0] == 0 && p_flag[1] == 1
&& p_flag[2] == 0) {
uniaxial = 1;
idir = 1;
} else if (p_flag[0] == 0 && p_flag[1] == 0
&& p_flag[2] == 1) {
uniaxial = 1;
idir = 2;
} else error->all("Invalid argument for fix nphug");
// triclinic hydrostatic compression
} else if (pstyle == TRICLINIC) {
if (p_start[0] == p_start[1] &&
p_start[0] == p_start[2] &&
p_start[3] == 0.0 &&
p_start[4] == 0.0 &&
p_start[5] == 0.0 )
uniaxial = 0;
else error->all("Invalid argument for fix nphug");
}
if (!tstat_flag)
error->all("Temperature control must be used with fix nphug");
if (!pstat_flag)
error->all("Pressure control must be used with fix nphug");
// create a new compute temp style
// id = fix-ID + temp
// compute group = all since pressure is always global (group all)
// and thus its KE/temperature contribution should use group all
int n = strlen(id) + 6;
id_temp = new char[n];
strcpy(id_temp,id);
strcat(id_temp,"_temp");
char **newarg = new char*[3];
newarg[0] = id_temp;
newarg[1] = (char *) "all";
newarg[2] = (char *) "temp";
modify->add_compute(3,newarg);
delete [] newarg;
tflag = 1;
// create a new compute pressure style
// id = fix-ID + press, compute group = all
// pass id_temp as 4th arg to pressure constructor
n = strlen(id) + 7;
id_press = new char[n];
strcpy(id_press,id);
strcat(id_press,"_press");
newarg = new char*[4];
newarg[0] = id_press;
newarg[1] = (char *) "all";
newarg[2] = (char *) "pressure";
newarg[3] = id_temp;
modify->add_compute(4,newarg);
delete [] newarg;
pflag = 1;
// create a new compute potential energy compute
n = strlen(id) + 3;
id_pe = new char[n];
strcpy(id_pe,id);
strcat(id_pe,"_pe");
newarg = new char*[3];
newarg[0] = id_pe;
newarg[1] = (char*)"all";
newarg[2] = (char*)"pe";
modify->add_compute(3,newarg);
delete [] newarg;
peflag = 1;
}
/* ---------------------------------------------------------------------- */
FixNPHug::~FixNPHug()
{
// temp and press computes handled by base class
// delete pe compute
if (peflag) modify->delete_compute(id_pe);
delete [] id_pe;
}
/* ---------------------------------------------------------------------- */
void FixNPHug::init()
{
// Call base class init()
FixNH::init();
// set pe ptr
int icompute = modify->find_compute(id_pe);
if (icompute < 0)
error->all("Potential energy ID for fix nvt/nph/npt does not exist");
pe = modify->compute[icompute];
}
/* ----------------------------------------------------------------------
compute initial state before integrator starts
------------------------------------------------------------------------- */
void FixNPHug::setup(int vflag)
{
FixNH::setup(vflag);
if ( v0_set == 0 ) {
v0 = compute_vol();
v0_set = 1;
}
if ( p0_set == 0 ) {
p0_set = 1;
if (uniaxial == 1)
p0 = p_current[idir];
else
p0 = (p_current[0]+p_current[1]+p_current[2])/3.0;
}
if ( e0_set == 0 ) {
e0 = compute_etotal();
e0_set = 1;
}
double masstot = group->mass(igroup);
rho0 = nktv2p*force->mvv2e*masstot/v0;
t_target = 0.01;
pe->addstep(update->ntimestep+1);
}
/* ----------------------------------------------------------------------
compute target temperature and kinetic energy
-----------------------------------------------------------------------*/
void FixNPHug::compute_temp_target()
{
t_target = t_current + compute_hugoniot();
ke_target = tdof * boltz * t_target;
pe->addstep(update->ntimestep+1);
}
/* ---------------------------------------------------------------------- */
double FixNPHug::compute_etotal()
{
double epot,ekin,etot;
epot = pe->compute_scalar();
if (thermo_energy) epot -= compute_scalar();
ekin = temperature->compute_scalar();
ekin *= 0.5 * tdof * force->boltz;
etot = epot+ekin;
return etot;
}
/* ---------------------------------------------------------------------- */
double FixNPHug::compute_vol()
{
if (domain->dimension == 3)
return domain->xprd * domain->yprd * domain->zprd;
else
return domain->xprd * domain->yprd;
}
/* ----------------------------------------------------------------------
Computes the deviation of the current point
from the Hugoniot in temperature units.
------------------------------------------------------------------------- */
double FixNPHug::compute_hugoniot()
{
double v,e,p;
double dhugo;
e = compute_etotal();
temperature->compute_vector();
if (uniaxial == 1) {
pressure->compute_vector();
p = pressure->vector[idir];
} else
p = pressure->compute_scalar();
v = compute_vol();
dhugo = (0.5 * (p + p0 ) * ( v0 - v)) /
force->nktv2p + e0 - e;
dhugo /= tdof * boltz;
return dhugo;
}
/* ----------------------------------------------------------------------
Compute shock velocity is distance/time units
------------------------------------------------------------------------- */
double FixNPHug::compute_us()
{
double v,p;
double eps,us;
temperature->compute_vector();
if (uniaxial == 1) {
pressure->compute_vector();
p = pressure->vector[idir];
} else
p = pressure->compute_scalar();
v = compute_vol();
// Us^2 = (p-p0)/(rho0*eps)
eps = 1.0 - v/v0;
if (eps < 1.0e-10) us = 0.0;
else if (p < p0) us = 0.0;
else us = sqrt((p-p0)/(rho0*eps));
return us;
}
/* ----------------------------------------------------------------------
Compute particle velocity is distance/time units
------------------------------------------------------------------------- */
double FixNPHug::compute_up()
{
double v;
double eps,us,up;
v = compute_vol();
us = compute_us();
// u = eps*Us
eps = 1.0 - v/v0;
up = us*eps;
return up;
}
// look for index in local class
// if index not found, look in base class
double FixNPHug::compute_vector(int n)
{
int ilen;
// n = 0: Hugoniot energy difference (temperature units)
ilen = 1;
if (n < ilen) return compute_hugoniot();
n -= ilen;
// n = 1: Shock velocity
ilen = 1;
if (n < ilen) return compute_us();
n -= ilen;
// n = 2: Particle velocity
ilen = 1;
if (n < ilen) return compute_up();
n -= ilen;
// index not found, look in base class
return FixNH::compute_vector(n);
}
/* ----------------------------------------------------------------------
pack restart data
------------------------------------------------------------------------- */
int FixNPHug::pack_restart_data(double *list)
{
int n = 0;
list[n++] = e0;
list[n++] = v0;
list[n++] = p0;
// call the base class function
n += FixNH::pack_restart_data(list+n);
return n;
}
/* ----------------------------------------------------------------------
calculate the number of data to be packed
------------------------------------------------------------------------- */
int FixNPHug::size_restart_global()
{
int nsize = 3;
// call the base class function
nsize += FixNH::size_restart_global();
return nsize;
}
/* ----------------------------------------------------------------------
use state info from restart file to restart the Fix
------------------------------------------------------------------------- */
void FixNPHug::restart(char *buf)
{
int n = 0;
double *list = (double *) buf;
e0 = list[n++];
v0 = list[n++];
p0 = list[n++];
e0_set = 1;
v0_set = 1;
p0_set = 1;
// call the base class function
buf += n*sizeof(double);
FixNH::restart(buf);
}
/* ---------------------------------------------------------------------- */
int FixNPHug::modify_param(int narg, char **arg)
{
if (strcmp(arg[0],"e0") == 0) {
if (narg < 2) error->all("Illegal fix nphug command");
e0 = atof(arg[1]);
e0_set = 1;
return 2;
} else if (strcmp(arg[0],"v0") == 0) {
if (narg < 2) error->all("Illegal fix nphug command");
v0 = atof(arg[1]);
v0_set = 1;
return 2;
} else if (strcmp(arg[0],"p0") == 0) {
if (narg < 2) error->all("Illegal fix nphug command");
p0 = atof(arg[1]);
p0_set = 1;
return 2;
}
return 0;
}

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