Topics

1

General / GCMC results not exactly matching with literature

« on: December 03, 2018, 01:19:18 PM »

Respected Prof. Dubbeldam

I am trying to replicate the adsorption isotherm on a zeolite, from the literature. In the literature, they have used Gibbs ensemble to study the adsorption on a zeolite. Using GCMC in RASPA, I tried to replicate the same thing. However, I am getting lower values compared to the literature. A constant difference of 0.5 mmol/g is being obtained at all pressures (0.1 bar to 10 bar). All the force fields, molecule models, and structure are the same. Could the difference in the ensemble, (or difference in the code) be the reason for this difference of 0.5 mmol/g?

Thanks and regards

2

Input files and parameters / Error while using "Grid" option

« on: October 28, 2018, 08:24:48 AM »

Dear Professor,

1. I am doing gas adsorption studies using GCMC.  To speed up my simulations, I have used the Grid option. By using the following input file, I am able to make energy grid.

Input file_1
SimulationType  MakeGrid

Forcefield      test
UseChargesFromCIFFile   yes

CutOff                        14.0

ChargeMethod                  Ewald
EwaldPrecision                1e-10

Framework 0
FrameworkName  framework
UnitCells 2 2 5
ExternalTemperature 298.0

NumberOfGrids 3
GridTypes H_s S_s S_com
SpacingVDWGrid 0.1
SpacingCoulombGrid 0.1
Input file end

I have used H2S molecule (4-3 Trappe model). There is one lone pair which is defined as an atom. So, in the .def file I have included "0 3 RIGID_BOND" command, to define the third bond. I have given S_com  notation for it.
Now, I used these grids for adsorption studies (GCMC), to speed the simulations. But I am getting a warning something like "Energy density interpolation probably not accurate enough". As I checked, Boltzmann relative error was very high for S_com only.  Other atoms doesn't have any error. The input file is as follows.

Input file_2
SimulationType                MonteCarlo
NumberOfCycles                50000
NumberOfInitializationCycles  50000
PrintEvery                    1000

Forcefield                    test
UseChargesFromCIFFile         yes

CutOff                        14.0

ChargeMethod                  Ewald
EwaldPrecision                1e-6

Framework 0
FrameworkName framework
UnitCells 2 2 5
ExternalTemperature 298.0
ExternalPressure 1e5

NumberOfGrids 3
GridTypes H_s S_s S_com
SpacingVDWGrid 0.1
SpacingCoulombGrid 0.1
UseTabularGrid yes

Component 0 MoleculeName                     H2S
            MoleculeDefinition               TraPPE
            TranslationProbability           0.5
            RotationProbability              0.5
            SwapProbability                  1.0
            CreateNumberOfMolecules          0
Input file end

I have used the correct grid, and the parameters are also the same. Can you suggest a way to overcome this error?


Thank you.

3

General / 'CrashRestart' taking long time

« on: October 17, 2018, 12:02:52 PM »

Dear Professor,

I am using RASPA to study the adsorption of a gas on a MOF. I have transferred my jobs from one cluster to another cluster, (after killing the jobs). In the new cluster, I have submitted the jobs, using 'CrashRestart    yes' command. I haven't changed anything else in the input file. I have 11 different files (each for a particular pressure). The simulations are taking almost 24 hours to pick up from where they have left. Also, the ones with high pressure (above 1 bar) are not running (I presume that it is still reading the Crash restart file). Is there a way I can speed up my calculations during using the 'Crash Restart'?

Thanks,

Regards,
Vardhan.