Difference in virial data from cp2k .log file and .stress file

[PWFYeung]

Summary

The virial outputs in the .log file and the .stress file by CP2K are different, but dpdata (fmt="cp2k/output") only reads the .log file. However, CP2K seems to output pv_virial in the .log file but print the pv_total in the .stress file. This might be problematic for generating virial data using dpdata.

Details

• CP2K virial_methods.F

STRESS TENSOR FROM .log FILE OF ONE SINGLE FRAME CALCULATION

  STRESS TENSOR [GPa]

            X               Y               Z
  X      -3.22841220      0.03875193      0.35205443
  Y       0.03875193     -2.99491119     -0.26930668
  Z       0.35205443     -0.26930668     -3.16014758

  1/3 Trace(stress tensor):  -3.12782366E+00

  Det(stress tensor)      :  -2.99521219E+01

.stress FILE OF THE SAME CALCULATION

#   Step   Time [fs]            xx [bar]            xy [bar]            xz [bar]            yx [bar]            yy [bar]            yz [bar]            zx [bar]            zy [bar]            zz [bar]
       0       0.000   -27535.1132302270      252.2330873873     3489.2605728168      252.2330873873   -25741.2101685947    -2388.1540627668     3489.2605728168    -2388.1540627668   -26927.8388906513

[wanghan-iapcm]

dpdata requires virial.
the stress may include kinetic contribution, which makes it different from virial.

[PWFYeung]

Thank you for your reply.

After digging into the issue, it seems that CP2K uses pv_total to change the box size. Also, LAMMPS appears to include the kinetic contribution when calculating the pressure of the system. There is also a paper explicitly saying that including the kinetic contribution gives more accurate results. Would it be possible that pv_total is a more ideal choice, or is there a reason for using pv_virial? Please do correct me if I'm wrong. I hope I am not causing any trouble.

References

• CP2K cell_opt_utils.F Keyword: ptens
• CP2K gopt_f77_methods.F Keyword: ptens
• LAMMPS Compute Pressure
• The Paper Discussing Virial