[CP2K-user] [CP2K:17456] Different values of stress tensor from FORCE_EVAL and MOTION sections duing MD

[Krack Matthias (PSI)]

Hi Abhishek

The total stress tensor including the contributions from the kinetic energy and the constraints (e.g. during a NpT run) is written to the .stress file whereas only the (zero-T) stress tensor is written to the CP2K output file, which are basically the derivatives of the total energy wrt to the cell parameters as needed during a CELL_OPT run.

HTH

Matthias

From: "cp2k at googlegroups.com" <cp2k at googlegroups.com> on behalf of Abhishek Sharma <asharma.ms.in at gmail.com>
Reply to: "cp2k at googlegroups.com" <cp2k at googlegroups.com>
Date: Wednesday, 10 August 2022 at 16:12
To: "cp2k at googlegroups.com" <cp2k at googlegroups.com>
Subject: [CP2K:17456] Different values of stress tensor from FORCE_EVAL and MOTION sections duing MD

Dear CP2K users,

I am trying to monitor the stress tensor in my ab initio MD simulation in NPT ensemble using CP2K version 7.1. I wrote two print sections, one in FORCE_EVAL section (to print stress file) as
...
  &PRINT
    &FORCES             ON
      FILENAME          =forces
    &END FORCES
    &STRESS_TENSOR      ON
        FILENAME        =stress
    &END STRESS_TENSOR
  &END PRINT
  STRESS_TENSOR         ANALYTICAL

and another in PRINT of MOTION section (to get pressure file)
...
        &STRESS
            &EACH
                MD 1
            &END
            FILENAME pressure
        &END STRESS

After running the job , I got following output in the stress file:
 STRESS TENSOR [GPa]
            X               Y               Z
  X       0.00106044     -0.00003023     -0.00393423
  Y      -0.00003023      0.01251158      0.00014630
  Z      -0.00393423      0.00014630      0.00717328
  1/3 Trace(stress tensor):   6.91510096E-03
  Det(stress tensor)      :  -9.84767286E-08
 EIGENVECTORS AND EIGENVALUES OF THE STRESS TENSOR
         -0.00086519      0.00909269      0.01251781

          0.89817098     -0.43935160     -0.01609565
         -0.00277868     -0.04228259      0.99910183
          0.43963755      0.89731954      0.03919782
  ==============================================================================
   Stress Tensor Components (GPW/GAPW)
                                                1/3 Trace           Determinant
   Kinetic Energy Stress                       1.22833622            0.02852337
   Basis Overlap Stress                        0.30458944            0.01186246
   ES + XC Stress                          -1736.32537740      ****************
   vdW correction (ff) Stress                 -0.00517761           -0.00000010
   Local Pseudopotential/Core Stress          -0.88167272           -0.56052030
   Nonlocal Pseudopotential Stress             2.92262879           20.96427765
   Exact Exchange Stress                      -0.00000000           -0.00000000
   Sum of Parts Stress                     -1732.75667328      ****************
   Total Stress                                0.00785295           -0.00000014
  ==============================================================================
 STRESS TENSOR [GPa]
            X               Y               Z
  X      -0.05130320      0.02112443     -0.15716038
  Y       0.02112443      0.07439468     -0.03381687
  Z      -0.15716038     -0.03381687      0.04697689
  1/3 Trace(stress tensor):   2.33561233E-02
  Det(stress tensor)      :  -1.75455374E-03

while in pressure file I got following output

#   Step   Time [fs]            xx [bar]            xy [bar]            xz [bar]            yx [bar]            yy [bar]            yz [bar]            zx [bar]            zy [bar]            zz [bar]
       0       0.000     2291.7724124002       -7.8261381151      -11.6256055821       -7.8261381151     2225.2853884787      190.2135354318      -11.6256055821      190.2135354318     2617.3106021379
       1       0.500     1721.2682620818      206.1262199908    -1539.1469767016      206.1262199908     2804.1547381410     -143.2394364947    -1539.1469767016     -143.2394364947     2958.6420055205

Both files have values different units (GPa in stress file and bar in pressure file). After converting values to same unit (say bar) the xx stress value 10.60 bar (0.00106044 GPa) does not match with the value of  2291.77 bar in the pressure file. Can you please help me to understand this ? Am I doing something wrong in my input file. The print output of cell vectors from the MOTION section is following:

#   Step   Time [fs]       Ax [Angstrom]       Ay [Angstrom]       Az [Angstrom]       Bx [Angstrom]       By [Angstrom]       Bz [Angstrom]       Cx [Angstrom]       Cy [Angstrom]       Cz [Angstrom]      Volume [Angstrom^3]
       0       0.000       16.9813194275        0.0000000000        0.0000000000        0.0009342941       17.1132431030        0.0000000000       -0.0392083935        0.0056124185       17.0369434357          4951.0285723949
       1       0.500       16.9878393880       -0.0026240361        0.0088682212       -0.0017097687       17.1090517191        0.0016270059       -0.0303270449        0.0072363688       17.0367331490          4951.6596469487

Many thanks ,
Abhishek



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