[Pw_forum] Pressure calculations with 2 different versions

[merlin.meheut at lmcp.jussieu.fr]

Hello,

I am experiencing quite a strange thing with pwscf: with the version
1.3.0 and 2.1.4, with an (almost) identical input file, I find 2 very
different calculated pressures  (even if almost everything else is the
same). Is that me or there is a difference between the two versions?

Below I report my two input files: for pw.1.3.0 and for 2.1.4 quantum
expresso. This is a calculation on the water molecule, so I take a big
unit cell for the molecules not to interact. I took the same initial
structure for the two calculations, except:
    the mixing_mode: it is potential for 1.3.0 (which is considered as
obsolete in the doc, but it converged anyway, so I don't see the
trouble), and plain for 2.1.4
    conv_thr : it is 10-18 in 1.3.0 and 10-9 in 2.1.4 , but as I
understood it is a formal question.

Moreover, on the same structure, if I make a structural relaxation
(calculation = RELAX), with pw.1.3.0 I find a final pressure of 0.1
kbars , whereas with the 2.1.4 I find almost the same relaxed structure,
but with a pressure of -20 kbars !

input for pw.1.3.0
 &control
       calculation = 'scf',
      restart_mode = 'from_scratch' ,
            prefix = 'VAP',
           disk_io = 'default' ,
    pseudo_dir     = './',
    outdir         = './',
    tprnfor        = .true.,
    tstress        = .true.,
/&end
 &system
    ibrav = 0, celldm(1)=30,
    nat = 3, ntyp = 2, ecutwfc = 80.0, ecutrho = 480.0,
/&end
 &electrons
   electron_maxstep = 30,
          conv_thr = 1.d-18,
       mixing_mode = 'potential',
       startingwfc = 'atomic',
       mixing_beta = 0.5,
   diagonalization = 'david_overlap',
/&end
 &ions
      ion_dynamics            = 'bfgs',
      potential_extrapolation = 'atomic',
/&end
ATOMIC_SPECIES
 O    15.9949    O.pbe
 H     1.0078    H.pbe2
ATOMIC_POSITIONS {angstrom}
O        -.010283269    .000000000    .000000000
H         .590805635    .770226149    .000000000
H         .590805635   -.770226149    .000000000
K_POINTS { gamma }
CELL_PARAMETERS { cubic }
  1.000000000   0.000000000    0.00000000
  0.000000000   1.000000000    0.00000000
  0.000000000   0.000000000    1.00000000

input for quantum expresso 2.1.4
  &control
       calculation = 'scf',
      restart_mode = 'from_scratch' ,
            prefix = 'VAP',
           disk_io = 'default' ,
    pseudo_dir     = './',
    outdir         = './scr/',
    tprnfor        = .true.,
    tstress        = .true.,
/&end
  &system
    ibrav =0, celldm(1)=30,
    nat = 3, ntyp = 2, ecutwfc =80.0,
    ecutrho=480.0

/&end
  &electrons
   electron_maxstep = 30,
          conv_thr = 1.d-9,
       mixing_mode = 'plain',
       startingwfc = 'atomic',
       mixing_beta = 0.5,
   diagonalization = 'david_overlap',
/&end
ATOMIC_SPECIES
  O    15.99491   O.pbe
  H     1.00783   H.pbe2
ATOMIC_POSITIONS {angstrom}
O        -.010283269    .000000000    .000000000
H         .590805635    .770226149    .000000000
H         .590805635   -.770226149    .000000000
K_POINTS {gamma}
CELL_PARAMETERS {CUBIC}
  1.000000000   0.000000000    0.00000000
  0.000000000   1.000000000    0.00000000
  0.000000000   0.000000000    1.00000000




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