From d0ba8e1dcbe7527914a6f5bb1dc74bf4fda8c5f9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tom=C3=A1=C5=A1=20Trnka?= <trnka@scm.com>
Date: Wed, 6 Jun 2018 17:24:26 +0200
Subject: [PATCH] Make omega_mass proportional to (N+1)kT

According to papers like Martyna, Tobias, Klein (JCP 1994,
doi:10.1063/1.467468 section II.F) and Martyna, Tuckerman, Tobias,
Klein (Mol. Phys. 1996, doi:10.1080/00268979600100761 section 2.5), the
mass of the cell parameters should be proportional to (Ndof + dim) / dim, or
in other words, Natoms + 1.
---
 src/fix_nh.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/fix_nh.cpp b/src/fix_nh.cpp
index 186376d952..170fd9db16 100644
--- a/src/fix_nh.cpp
+++ b/src/fix_nh.cpp
@@ -798,7 +798,7 @@ void FixNH::setup(int vflag)
 
   if (pstat_flag) {
     double kt = boltz * t_target;
-    double nkt = atom->natoms * kt;
+    double nkt = (atom->natoms + 1) * kt;
 
     for (int i = 0; i < 3; i++)
       if (p_flag[i])
@@ -1826,7 +1826,7 @@ void FixNH::nhc_press_integrate()
   // Update masses, to preserve initial freq, if flag set
 
   if (omega_mass_flag) {
-    double nkt = atom->natoms * kt;
+    double nkt = (atom->natoms + 1) * kt;
     for (int i = 0; i < 3; i++)
       if (p_flag[i])
         omega_mass[i] = nkt/(p_freq[i]*p_freq[i]);