[CP2K-user] [CP2K:13690] Wrong density prediction in NpT AIMD

[Thomas Kühne]

Dear Mostafa, 

your simulation is way too short. Equilibrating the density needs many dozens of ps of simulation, 
and much more so since you are using the default 1ps time constant for the barostat. My 
suggestion is to reduce that to 100 fs and rerun your simulation for at least 25 ps. Also, you were 
missing to add the VdW contribution of the wB97X XC functional. 

Cheers, 
Thomas

> Am 29.07.2020 um 14:57 schrieb Abedi, Mostafa <mostaf... at brown.edu>:
> 
> Hi Everyone,
> I've performed NpT AIMD simulations for a system containing 8 CH4 molecules. The system was equilibrated using 2 ps NVT (300K) followed by 2 ps NVE. For some reason, the predicted density keeps decreasing and getting away from the correct value (The correct density is 0.232 g/cm3):
> 
>     Time evaluation of density for a box of 8 CH4 at 300 K and 400 bar
> <density.PNG>
> The wB97XD/TZVP-MOLOPT-GTH level of theory was used for the electronic structure part. Unfortunately, there is not much in the literature for this system (or similar systems) to get some ideas for the level of theory. To my mind, it could be due to the wrong prediction of the intermolecular repulsive interactions (vdW dispersion forces). But, there might be some other parameters in the simulations that can cause this issue. Any suggestions or advice for fixing this issue would be greatly appreciated. Many thanks. 
> 
> Best,
> Mostafa
> 
> Input file:
> &GLOBAL
>   PROJECT methane
>   RUN_TYPE MD   
>   WALLTIME 10000000
>   IOLEVEL  LOW          
> &END GLOBAL
> 
> &FORCE_EVAL
>  STRESS_TENSOR ANALYTICAL
>   METHOD Quickstep
>   &DFT
>     BASIS_SET_FILE_NAME BASIS_MOLOPT
>     POTENTIAL_FILE_NAME GTH_POTENTIALS             
>     CHARGE 0
>     MULTIPLICITY 1
>     &MGRID
>        CUTOFF [Ry] 400 
>     &END
>     &QS
>        METHOD GPW 
>        EPS_DEFAULT 1.0E-10 
>        EXTRAPOLATION ASPC 
>     &END
>     &POISSON
>        PERIODIC XYZ 
>        POISSON_SOLVER PERIODIC
>     &END
>     &SCF  
>       &PRINT
>         &RESTART OFF
>         &END
>       &END         
>       SCF_GUESS ATOMIC 
>       MAX_SCF 300
>       EPS_SCF 1.0E-6 
>       &OT
>         PRECONDITIONER FULL_SINGLE_INVERSE
>         MINIMIZER CG
>       &END OT
>       &OUTER_SCF 
>         MAX_SCF 300
>         EPS_SCF 1.0E-6 
>       &END
>     &END SCF
>     &XC
>       &XC_FUNCTIONAL
>         &LIBXC
>           FUNCTIONAL XC_HYB_GGA_XC_WB97X_D
>         &END LIBXC
>       &END XC_FUNCTIONAL
>     &END XC
>   &END DFT
>   &SUBSYS
>     &CELL 
>       ABC [angstrom] 9.71 9.71 9.71
>       PERIODIC XYZ
>     &END CELL
>     &TOPOLOGY
>       COORD_FILE_NAME methane.xyz <http://methane.xyz/>
>       COORD_FILE_FORMAT XYZ
>     &END
>     &KIND H
>       ELEMENT H
>       BASIS_SET TZVP-MOLOPT-GTH
>       POTENTIAL GTH-PBE-q1
>     &END KIND
>     &KIND C
>       ELEMENT C
>       BASIS_SET TZVP-MOLOPT-GTH
>       POTENTIAL GTH-PBE-q4
>     &END KIND
>   &END SUBSYS
>   &PRINT
>     &FORCES ON
>      FILENAME forces 
>     &END
>   &END
> &END FORCE_EVAL
> 
> &MOTION
>  &GEO_OPT
>    OPTIMIZER BFGS 
>    MAX_ITER  1000
>    MAX_DR    [bohr] 0.003 
>    &BFGS
>    &END
>  &END
>   &MD
>    ENSEMBLE NPT_I
>    STEPS 15000
>    TIMESTEP 0.5
>    TEMPERATURE 300
>    &BAROSTAT
>     PRESSURE 400
>    &END BAROSTAT
>    &THERMOSTAT
>     REGION MASSIVE
>     TYPE CSVR
>     &CSVR
>     TIMECON 50
>     &END CSVR
>    &END THERMOSTAT
>  &END MD
>  &PRINT
>    &TRAJECTORY
>     FORMAT XYZ 
>    &END
>    &CELL
>     FILENAME cell 
>    &END
>  &END
> &END MOTION
> 
> 
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==============================
Thomas D. Kühne
Dynamics of Condensed Matter
Chair of Theoretical Chemistry
University of Paderborn
Warburger Str. 100
D-33098 Paderborn
Germany
tdku... at mail.upb.de
+49/(0)5251/60-5726

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