From a554d22cd19dc3c68e81dface492bb7cf0c48141 Mon Sep 17 00:00:00 2001
From: sjplimp <sjplimp@f3b2605a-c512-4ea7-a41b-209d697bcdaa>
Date: Fri, 8 Feb 2008 20:00:47 +0000
Subject: [PATCH] git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@1472
 f3b2605a-c512-4ea7-a41b-209d697bcdaa

---
 src/fix_langevin.cpp | 11 +++++++++--
 src/fix_langevin.h   |  1 +
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/fix_langevin.cpp b/src/fix_langevin.cpp
index 9a31cb89fd..61307e6d74 100644
--- a/src/fix_langevin.cpp
+++ b/src/fix_langevin.cpp
@@ -58,6 +58,7 @@ FixLangevin::FixLangevin(LAMMPS *lmp, int narg, char **arg) :
   flagx = flagy = flagz = 1;
   for (int i = 1; i <= atom->ntypes; i++) ratio[i] = 1.0;
   iregion = -1;
+  scalefactor = 1.0;
 
   int iarg = 7;
   while (iarg < narg) {
@@ -76,9 +77,15 @@ FixLangevin::FixLangevin(LAMMPS *lmp, int narg, char **arg) :
       ratio[itype] = scale;
       iarg += 3;
     } else if (strcmp(arg[iarg],"region") == 0) {
+      if (iarg+2 > narg) error->all("Illegal fix langevin command");
       iregion = domain->find_region(arg[iarg+1]);
       if (iregion == -1) error->all("Fix langevin region ID does not exist");
       iarg += 2;
+    } else if (strcmp(arg[iarg],"weight") == 0) {
+      if (iarg+2 > narg) error->all("Illegal fix langevin command");
+      scalefactor = atof(arg[iarg+1]);
+      if (scalefactor <= 0.0) error->all("Illegal fix langevin command");
+      iarg += 2;
     } else error->all("Illegal fix langevin command");
   }
 }
@@ -114,7 +121,7 @@ void FixLangevin::init()
 
   for (int i = 1; i <= atom->ntypes; i++) {
     gfactor1[i] = - atom->mass[i] / t_period / force->ftm2v;
-    gfactor2[i] = sqrt(atom->mass[i]) * 
+    gfactor2[i] = scalefactor * sqrt(atom->mass[i]) * 
       sqrt(24.0*force->boltz/t_period/update->dt/force->mvv2e) / force->ftm2v;
     gfactor1[i] *= 1.0/ratio[i];
     gfactor2[i] *= 1.0/sqrt(ratio[i]);
@@ -203,7 +210,7 @@ void FixLangevin::reset_target(double t_new)
 void FixLangevin::reset_dt()
 {
   for (int i = 1; i <= atom->ntypes; i++) {
-    gfactor2[i] = sqrt(atom->mass[i]) * 
+    gfactor2[i] = scalefactor * sqrt(atom->mass[i]) * 
       sqrt(24.0*force->boltz/t_period/update->dt/force->mvv2e) / force->ftm2v;
     gfactor2[i] *= 1.0/sqrt(ratio[i]);
   }
diff --git a/src/fix_langevin.h b/src/fix_langevin.h
index 1deeb84926..2cd90ef2db 100644
--- a/src/fix_langevin.h
+++ b/src/fix_langevin.h
@@ -34,6 +34,7 @@ class FixLangevin : public Fix {
   double t_start,t_stop,t_period;
   int flagx,flagy,flagz,iregion;
   double *gfactor1,*gfactor2,*ratio;
+  double scalefactor;
 
   int nlevels_respa;
   class RanMars *random;