Dear RASPA users,
I tried to compare MD and MC runs in NPT ensemble for 2-methylbutane molecules which forcefield is attached to Raspa as an example. I did not modify the force field but I am not able to reach the same density in MC and MD (in MD the density is lower by 100 kg/m^3). I tried simulations at different state point and I was not able to match MC and MD Raspa results. I also tried simulations of different molecules and my results match only for water all other molecules differed in density.
I had found that MD results are changes when I am using the option "ComputeMolecularPressure yes". I can't see why there should be any change in density with this option if the barostat is working properly. If this option is necessary for barostat, then the NPT run should not be performed without this command.
Attached you can find my MD simulation script (system did not allow me to attach the file itself). I will be glad for your advice. I believed that problem is in my simulation settings.
SimulationType MolecularDynamics
NumberOfCycles 50000000
NumberOfInitializationCycles 1000
NumberOfEquilibrationCycles 10000
PrintEvery 100
RestartFile no
InitEnsemble NVT
RunEnsemble NPT
TimeStep 0.001
Forcefield local
CutOff 12
ChargeMethod Ewald
CutOffVDW 12
CutOffCoulomb 12
Box 0
BoxLengths 37 37 37
ExternalTemperature 293.15
ComputeMolecularPressure yes
ExternalPressure 101325
Movies yes
WriteMoviesEvery 1000
Component 0 MoleculeName 2-methylbutane
MoleculeDefinition local
ReinsertionProbability 1.0
TranslationProbability 1.0
CreateNumberOfMolecules 256
I tried to compare MD and MC runs in NPT ensemble for 2-methylbutane molecules which forcefield is attached to Raspa as an example. I did not modify the force field but I am not able to reach the same density in MC and MD (in MD the density is lower by 100 kg/m^3). I tried simulations at different state point and I was not able to match MC and MD Raspa results. I also tried simulations of different molecules and my results match only for water all other molecules differed in density.
I had found that MD results are changes when I am using the option "ComputeMolecularPressure yes". I can't see why there should be any change in density with this option if the barostat is working properly. If this option is necessary for barostat, then the NPT run should not be performed without this command.
Attached you can find my MD simulation script (system did not allow me to attach the file itself). I will be glad for your advice. I believed that problem is in my simulation settings.
SimulationType MolecularDynamics
NumberOfCycles 50000000
NumberOfInitializationCycles 1000
NumberOfEquilibrationCycles 10000
PrintEvery 100
RestartFile no
InitEnsemble NVT
RunEnsemble NPT
TimeStep 0.001
Forcefield local
CutOff 12
ChargeMethod Ewald
CutOffVDW 12
CutOffCoulomb 12
Box 0
BoxLengths 37 37 37
ExternalTemperature 293.15
ComputeMolecularPressure yes
ExternalPressure 101325
Movies yes
WriteMoviesEvery 1000
Component 0 MoleculeName 2-methylbutane
MoleculeDefinition local
ReinsertionProbability 1.0
TranslationProbability 1.0
CreateNumberOfMolecules 256