[Pw_forum] vc-relax : total force does not converge

[Jiseok Kim]

Dear, Dr. Kumar

Yes. I checked the geometry before and after the 'relax' which looks ok ...
The atomic distance between neighboring atoms about 12A along x-direction
and about 24A along y-direction..
The vacuum region along x-direction might not be large enough but I
believe it wouldn't be a problem having considered that the 10~15A of
vacuum region usually is accepted. (Please correct me if I'm wrong.)
Could I ask what you mean by 'it is far from the Si-H system' ?

Thank you very much.

Best regards,

Jiseok Kim

On 9/5/12 2:51 AM, "pw_forum-request at pwscf.org"
<pw_forum-request at pwscf.org> wrote:

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>Today's Topics:
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>   1. Re: Pw_forum Digest, Vol 63, Issue 8 (Ramesh Kumar)
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>----------------------------------------------------------------------
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>Message: 1
>Date: Wed, 5 Sep 2012 09:02:11 +0530
>From: Ramesh Kumar <rameshchitumalla at gmail.com>
>Subject: Re: [Pw_forum] Pw_forum Digest, Vol 63, Issue 8
>To: pw_forum at pwscf.org
>Message-ID:
>    <CAO1fJnvo6EhnZUdMYhURsg2Y9fDQimng16PYiqLUOUCgfCXFFw at mail.gmail.com>
>Content-Type: text/plain; charset="iso-8859-1"
>
>Dear JISEOK KIM,
>
>Did you check/visualize your geometry ?
>
>The Box is too small and it is far from the Si-H system.
>
>
>
>
>> I'm having a difficulty on a geometry optimization using 'vc-relax'.
>> I searched forum threads and followed various suggestions but the 'Total
>> force' still does not converge..
>> (but the pressures seems to be converged)
>>
>> The job steps I've taken as follows,
>>
>> 1. optimized k-point and ecutwfc.
>> 2. optimized lattice parameter using Murnaghan fitting.
>> 3. 'relax' the geometry using the lattice constant obtained from step2,
>>
>> ----------------------------------------------
>> &control
>>   calculation     = 'relax',
>>   restart_mode    = 'from_scratch',
>>   prefix          = '$NAME',
>>   pseudo_dir      = '$PSEUDO_DIR/',
>>   outdir          = '$OUT_DIR/',
>>   wf_collect      = .TRUE.
>>   tstress         = .TRUE.
>>   tprnfor         = .TRUE.
>>   etot_conv_thr   = 1.d-7
>>   forc_conv_thr   = 1.d-6
>>   nstep           = 1000
>> /
>> &system
>>   ibrav           = 0,
>>   celldm(1)       = 10.3345
>>   nat             = 18,
>>   ntyp            = 2,
>>   ecutwfc         = 80.0,
>> /
>> &electrons
>>   diagonalization = 'cg',
>>   mixing_mode     = 'plain',
>>   mixing_beta     = 0.7,
>>   conv_thr        = 1.0d-10,
>> /
>> &ions
>>   ion_dynamics    = 'bfgs'
>>   bfgs_ndim       = 3
>> /
>> ATOMIC_SPECIES
>> Si 28.086  Si.pbe-rrkj.UPF
>> H  1.0079  H.pbe-vbc.UPF
>> CELL_PARAMETERS
>>   ..........
>>
>      ..........
>
>> K_POINTS automatic
>> 1 1 16 0 0 0
>> ----------------------------------------------
>>
>>
>> 4. check if 'Total force' is converged -> OK.
>> 5. Take the final atomic coordinates from step4.
>> 6. Run 'vc-relax' as,
>>
>> ----------------------------------------------
>> &control
>>   calculation     = 'vc-relax',
>>   restart_mode    = 'from_scratch',
>>   prefix          = '$NAME',
>>   pseudo_dir      = '$PSEUDO_DIR/',
>>   outdir          = '$OUT_DIR/',
>>   wf_collect      = .TRUE.
>>   tstress         = .TRUE.
>>   tprnfor         = .TRUE.
>>   etot_conv_thr   = 1.d-6
>>   forc_conv_thr   = 1.d-6
>>   nstep           = 10000
>> /
>> &system
>>   ibrav           = 0,
>>   celldm(1)       = 10.3345
>>   nat             = 18,
>>   ntyp            = 2,
>>   ecutwfc         = 80.0,
>>   ecfixed         = 70.0,
>>   qcutz           = 150.0,
>>   q2sigma         = 4.0,
>> /
>> &electrons
>>   diagonalization = 'cg',
>>   mixing_mode     = 'plain',
>>   mixing_beta     = 0.7,
>>   conv_thr        = 1.0d-10,
>> /
>> &ions
>>   ion_dynamics    = 'bfgs'
>>   bfgs_ndim       = 3
>> /
>> &cell
>>   cell_dynamics   = 'bfgs'
>>   press_conv_thr  = 0.1d0
>>   press           = 0.d0
>>   cell_factor     = 2.d0
>> /
>> ATOMIC_SPECIES
>> Si 28.086  Si.pbe-rrkj.UPF
>> H  1.0079  H.pbe-vbc.UPF
>> ---------
>>
>   ----------
>
>> K_POINTS automatic
>> 1 1 16 0 0 0
>> ----------------------------------------------
>>
>>
>>
>-- 
>*With Best Regards:
>
>*
>*CH. Ramesh Kumar
>Senior Research Fellow,
>Computational Chemistry Lab,
>Indian Institute of Chemical Technology(IICT),*
>*Tarnaka, **
>Hyderabad.
>*
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