Specifying pressure in Gibbs Ensemble Monte Carlo Simulations

[Vyacheslav Bryantsev]

Dear CP2K Developers,

I am running Gibbs Ensemble Monte Carlo example from

https://www.cp2k.org/howto:gemc

I have a question of why the PRESSURE in the MC section needs to be specified for the GEMC_NVT ensemble. 

I have a single component H2O system, and as long as temperature is defined in the Monte Carlo simulations, all the other intensive variables, such as  pressure should come out as the result of the simulation, not the input parameter.

Could you please explain the meaning of the PRESSURE in this case?

If I do not specify it, I get the error as shown below.

The MC block for one of the boxes is also shown below.

Thank you,

Slava

Vyacheslav Bryantsev

*******************************************************************************
 *   ___                                                                       *
 *  /   \                                                                      *
 * [ABORT]                                                                     *
 *  \___/      Value requested, but no value set getting value from keyword    *
 *    |                           PRESSURE of section MC                       *
 *  O/|                                                                        *
 * /| |                                                                        *
 * / \                                        input/input_section_types.F:1097 *
 *******************************************************************************

The MC block for one of the boxes is shown below.

&MOTION
  &MC
    ENSEMBLE GEMC_NVT
    TEMPERATURE 398.0
    IPRINT 1
    LBIAS no
    LSTOP yes
    NMOVES 8
    NSWAPMOVES 640
    NSTEP 500
    PRESSURE 1.013
    RESTART no
    BOX2_FILE_NAME GEMC_NVT_box2.inp
    RESTART_FILE_NAME mc_restart_1
    ETA 0.0
!    VIRIAL_TEMPS 300.0
    &MOVE_PROBABILITIES
      PMSWAP 0.20
      PMTRAION 0.30
      PMTRANS 0.60
      PMVOLUME 0.05
      PMHMC 0.0
      PMAVBMC 0.0
      &MOL_PROBABILITIES
        PMAVBMC_MOL 1.0
        PMSWAP_MOL 1.0
        PMTRAION_MOL 1.0
        PMTRANS_MOL 1.0
        PMROT_MOL 1.0
      &END MOL_PROBABILITIES
      &BOX_PROBABILITIES
        PMVOL_BOX 1.0
        PMHMC_BOX 1.0
      &END BOX_PROBABILITIES
    &END MOVE_PROBABILITIES
    &MOVE_UPDATES
      IUPTRANS 100
      IUPVOLUME 100
    &END MOVE_UPDATES
    &MAX_DISPLACEMENTS
      &MOL_DISPLACEMENTS
        RMDIHEDRAL 3.0
        RMANGLE 3.0
        RMBOND 0.074
        RMROT 26.0
        RMTRANS 0.38
      &END MOL_DISPLACEMENTS
      &BOX_DISPLACEMENTS
        RMVOLUME 100.5
      &END BOX_DISPLACEMENTS
    &END MAX_DISPLACEMENTS
    &AVBMC
      AVBMC_ATOM 1
      AVBMC_RMIN 1.0
      AVBMC_RMAX 5.0
      PBIAS 0.5
    &END AVBMC
  &END MC
&END MOTION