[DFTB-Plus-User] What do the Pressure indicate?

[Ben Hourahine]

Dear xiaobao,

the difference is due to the data in md.out including the contribution
to the pressure from the kinetic energy of the atomic motion in the
system, while the standard output only shows the virial presure. We will
clarify the labels in the output data for the next release.

Regards

Ben

On 21/01/16 07:31, jsxz wrote:
> Dear all,
> I am running the SCC-DFTB with the VelocityVerlet method,
> Driver = VelocityVerlet {
> MovedAtoms = 1:-1
> Steps = 10000 KeepStationary = Yes TimeStep [fs] = 1.0
> MDRestartFrequency = 1 OutputPrefix = "geom.out" Thermostat = None {}
> Velocities [AA/ps] = { <<< "velocity.txt" } ConvergentForcesOnly = No }
> I find the pressure in md.out different from that in out.log, Which
> are as follows:
> *In the file: md.out*
> MD step: 0 *Pressure: -0.311743E-05 au -0.917179E+08 Pa*Potential
> Energy: -494.7211745146 H -13462.0481 eV MD Kinetic Energy:
> 9.5186349932 H 259.0152 eV Total MD Energy: -485.2025395214 H
> -13203.0329 eV MD Temperature: 0.0221106504 au 6981.9828 K
> ...
> ...
> MD step: 10000 *Pressure: -0.339071E-05 au -0.997580E+08 Pa*Potential
> Energy: -490.2082249886 H -13339.2445 eV MD Kinetic Energy:
> 4.9888127115 H 135.7525 eV Total MD Energy: -485.2194122771 H
> -13203.4920 eV MD Temperature: 0.0115884151 au 3659.3277 K
> *In the file: out.log*
> ********************************************************************************
> ** Geometry step: 0
> ********************************************************************************
> MAXNEIGHBORS: 2561 iSCC Total electronic Diff electronic SCC error 1
> -0.51582486E+03 0.00000000E+00 0.11868403E-04 2 -0.51582486E+03
> -0.10265921E-09 0.78293993E-05 scc total CPU: 7.38 Wall: 7.42 Total
> Energy: -494.7011653169 H Total Mermin free energy: -494.7211745146 H
> force total CPU: 0.99 Wall: 1.01 Volume: 0.172487E+07 au^3 *Pressure:
> 0.561541E-06 au 0.165211E+08 Pa*>> Charges saved for restart in
> charges.bin MD Temperature:: 0.0221106504 H 6981.9828 K MD Kinetic
> Energy: 9.5186349932 H Total MD Energy: -485.2025395214 H
> *...*
> *...*
> ********************************************************************************
> ** Geometry step: 10000
> ********************************************************************************
> MAXNEIGHBORS: 2561 iSCC Total electronic Diff electronic SCC error 1
> -0.51191555E+03 0.00000000E+00 0.14908229E+00 2 -0.51173238E+03
> 0.18317087E+00 0.40312730E+00 3 -0.51193732E+03 -0.20493450E+00
> 0.67927614E-01 4 -0.51193530E+03 0.20158403E-02 0.96219530E-01 5
> -0.51194305E+03 -0.77460598E-02 0.14910683E-01 6 -0.51194297E+03
> 0.77176499E-04 0.72112883E-02 7 -0.51194288E+03 0.92423888E-04
> 0.22124927E-01 8 -0.51194311E+03 -0.23527271E-03 0.57641324E-02 9
> -0.51194310E+03 0.79870361E-05 0.34686526E-02 10 -0.51194310E+03
> 0.80522580E-06 0.12716026E-02 11 -0.51194314E+03 -0.37330772E-04
> 0.44577841E-03 12 -0.51194314E+03 0.33205728E-05 0.23560681E-03 13
> -0.51194314E+03 0.16375881E-05 0.80152822E-04 14 -0.51194314E+03
> -0.24583005E-06 0.51844159E-04 15 -0.51194313E+03 0.45254882E-06
> 0.64249756E-05 scc total CPU: 54.94 Wall: 54.97 Total Energy:
> -490.1918593225 H Total Mermin free energy: -490.2082249886 H force
> total CPU: 0.81 Wall: 0.80 Volume: 0.172487E+07 au^3 *Pressure:
> -0.146252E-05 au -0.430288E+08 Pa*>> Charges saved for restart in
> charges.bin MD Temperature:: 0.0115884151 H 3659.3277 K MD Kinetic
> Energy: 4.9888127115 H Total MD Energy: -485.2194122771 H Molecular
> dynamics completed MD information accumulated in md.out program total
> CPU: ******** Wall: ********
> What do the pressures in the two files indicate, respectively?
> Thanks!
> xiaobao
>
>
>  
>
>
>
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-- 
      Dr. B. Hourahine, SUPA, Department of Physics,
    University of Strathclyde, John Anderson Building,
            107 Rottenrow, Glasgow G4 0NG, UK.
    +44 141 548 2325, benjamin.hourahine at strath.ac.uk

2013/4 THE Awards Entrepreneurial University of the Year
      2012/13 THE Awards UK University of the Year

   The University of Strathclyde is a charitable body,
        registered in Scotland, number SC015263

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