[Pw_forum] ecfixed makes the volume different?

[Riping WANG]

Dear Forum,


Could anyone give me some hints about how to adjust "qcutz,q2sigma,ecfixed"
in vc-cp?

I have some difficulties. After wave function initialization, the input file
are for zero pressure zero temperature are following.
(After zero pressure zero temperature, I will elevate temperature with
verlet algorithm.)
 But when I use different ecfixed with fixed qcutz and q2sigma, the volumes
at equilibrium are different.
some is close to that without "qcutz,q2sigma,ecfixed" used. some are 100 (
toal around 3000) different from that without "qcutz,q2sigma,ecfixed" used.
(In my case, I am sure the fnosep, wmass, and emass is good enough.)

I attached the voluem evolution figure. In the figure, from step 200-1200 is
belong to the following input file.
before 200 step is wave initialization, after 1200 step, I increased
temperature.


Thank you very much!

WANG Riping
2011.3.7



&control
    calculation = 'vc-cp' ,
    prefix = 'SiO2-mog' ,
    restart_mode = 'restart' ,
    nstep = 1000 ,
    iprint = 1 ,
    isave = 10 ,
    dt = 5.0 ,
    ndr = 51 ,
    ndw = 52 ,
    tstress = .TRUE. ,
    tprnfor = .TRUE. ,
    saverho = .TRUE. ,
    disk_io = 'high' ,
    /ekin_conv_thr = 1.0d-3 ,
    /etot_conv_thr = 5.0d-3 ,
    /forc_conv_thr = 1.0d-2 ,
    pseudo_dir ='~/espresso/pseudo' ,
    outdir = './' ,
 /
 &system
    ibrav = 14 ,
    celldm(1) = 16.021289268 ,
    celldm(2) = 0.558448710 ,
    celldm(3) = 1.245135500 ,
    celldm(4) = -0.000028830 ,
    celldm(5) = -0.007432130 ,
    celldm(6) = 0.000064680 ,
    nat = 36 ,
    ntyp = 2 ,
    ecutwfc = 30 ,
    ecutrho = 240.0 ,
    nr1b = 16 ,
    nr2b = 16 ,
    nr3b = 16 ,
    qcutz = 150.0 ,
    q2sigma = 2 ,
    ecfixed = 16.8 ,
 /
 &electrons
    electron_dynamics = 'sd' ,
    emass = 400 ,
    emass_cutoff = 3. ,
/
&ions
    ion_dynamics = 'sd' ,
/
&cell
    cell_dynamics = 'pr' ,
    press = 0 ,
    wmass = 300 ,
 /
ATOMIC_SPECIES
   O  16.00 O.pbe-van_ak.UPF
  Si  28.00 Si.pbe-n-van.UPF
ATOMIC_POSITIONS (crystal)
 ...






-- 
******************************************************************************
WANG Riping
Ph.D student,
Institute for Study of the Earth's Interior,Okayama University,
827 Yamada, Misasa, Tottori-ken 682-0193, Japan
Tel: +81-858-43-3739(Office), 1215(Inst)
E-mail: wang.riping.81 at gmail.com
******************************************************************************
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