[Pw_forum] Re: Problem with vc -relax

[cesards at msi.umn.edu]

Dear Shruba,


I notice that your input doe not contains the varables "dt" in &CONTROL
namelist (dt = 80.0 is recommended for start) and "wmass" in &CELL
namelist (wmass =  0.001 , for example). If get large negative stresses in
the first MD step, try to reduce celldm(1).

It is normal for the cell volume to oscilate. Things are going wrong only
if the amplitude of oscilations are increasing.


Yours,


Cesar R.S. da Silva




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> Hi all,
>      I was trying to run vc-relax calculation for srfeo3 (
> antiferromagnetic
> mettalic ) system,  the problem I was facing for a unit cell it is running
> for 3-4 days in processor , where as a single point 'scf' calculation is
> taking only 5 minutes, the scf calculation is giving very nice agreement
> with experimental data , but for vc -relax  i checked the cell volume was
> decresing first then it started exapnding after a certain point, this is
> my
> input file . If any one can help me in this matter that will be really
> great
> help, I am using same cutoff and other parameters required for scf
>
> &CONTROL
>
> calculation = 'vc-relax',
>
> restart_mode = 'from_scratch',
>
> tstress = .TRUE.,
>
> tprnfor = .TRUE.,
>
> prefix = 'relax',
>
> pseudo_dir = '/............./',
>
> outdir='/................../'
>
> /
>
> &SYSTEM
>
> ibrav = 1,
>
> celldm(1) = 7.3
>
> nat =5,
>
> ntyp =3,
>
> ecutwfc = 45,
>
> ecutrho = 360,
>
> nspin=2,
>
> nelec=44
>
> nelup=26,
>
> neldw=18,
>
> nbnd=52,
>
> occupations = 'smearing',
>
> smearing ='marzari-vanderbilt',
>
> degauss=0.03,
>
> qcutz=150., q2sigma=2.0,ecfixed=10.0
>
> /
>
> &ELECTRONS
>
> electron_maxstep =200,
>
> emass =1000.d0,
>
> emass_cutoff = 4.d0,
>
> orthogonalization = 'Gram-Schmidt',
>
> startingwfc ='atomic',
>
> n_inner = 8,
>
> tcg = .TRUE.,
>
> passop=0.3,
>
> maxiter = 250,
>
> conv_thr=1.d-6,
>
> /
>
> &IONS
>
> ion_dynamics = 'damp',
>
> ion_damping = 0.,
>
> ion_positions = 'from_input',
>
> ion_temperature = 'not_controlled',
>
> /
>
> &CELL
>
> cell_dynamics = 'damp-w'
>
> /
>
> ATOMIC_SPECIES
>
> Fe 55.85 Fe.pbe-sp-van.UPF
>
> Sr 87.62 Sr.pbe-nsp-van.UPF
>
> O 16.00 O.pbe-van-bm.UPF
>
> ATOMIC_POSITIONS
>
> Sr 0.000 0.000 0.010
>
> Fe 0.500 0.500 0.500
>
> O 0.000 0.500 0.500
>
> O 0.500 0.500 0.000
>
> O 0.500 0.000 0.500
>
> K_POINTS {automatic}
>
> 8 8 8 1 1 1
>
> Thanks in advance , looking forward for your reply
>                                 shruba
>
> --
> shruba gangopadhyay
> graduate student
> department of chemistry
> university of central florida
> orlando, FL-32826
> 'friendship doubles joys and reduces sorrows by half' (Francis Bacon).
>