[gmx-users] Temperature control in fix gcmc with fix rigid/nvt/small

[Youzhi Hao]

hi,

I'm trying to do gcmc simulation of rigid CH4 molecules adsorption isotherms
in clay minerals 

by using fix gcmc with fix rigid/nvt/small.

The coulomb potential was calculated by PPPM.

The fix rigid/nvt/small was combined with fix_modify dynamic/dof yes 

and fix_modify temp as the LAMMPS Manuals says.

 

However, as the simulation going on (after a long time), the CH4 molecules
were just kept adding to the system, 

leading the pressure far higher than the pressure specified in fix gcmc
command.

Also, the system temperature continues increasing up, higher than the
specified temperature.

The fix rigid/nvt/small command seems did not thermostat well. 

So, what's the reason lying beneath this unusual phenomenon?

 

Part of my input file is :

variable temp  equal  363.15

variable press  equal  100.00

variable fug_coeff equal 0.934

molecule  ch4  mol.ch4.txt  #full atom methane molecule

compute Temp_methane methane temp/com

compute_modify Temp_methane dynamic/dof yes

fix  mrsnvt  methane  rigid/nvt/small  molecule  temp ${temp} ${temp} 100.0
mol ch4

fix_modify  mrsnvt  dynamic/dof  yes

fix_modify  mrsnvt  temp  Temp_methane

fix  1  methane  gcmc  1000  1000 500 0 2949499 ${temp} -0.28 0.5 mol ch4  &


      maxangle 180 rigid mrsnvt pressure ${press}  fugacity_coeff ${
fug_coeff } full_energy

run 5000000

 

Best regards.

Youzhi Hao