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

[Alex]

It may come as a huge surprise, but this is a mailing list for a 
different software package. ;)


On 6/19/2017 12:49 AM, Youzhi Hao wrote:
> 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
>