[CP2K-user] Wrong density prediction in NpT AIMD

[Abedi, Mostafa]

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*
[image: 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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