[Pw_forum] question about the stress in relax process

[xirainbow]

Dear Wang:
All these parameters in the blow article may influence the relaxed
structure.
*《Designing meaningful density functional theory calculations in materials
science—a prime.》*
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***
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On Mon, Sep 20, 2010 at 6:02 PM, Wang Di <didi5158 at gmail.com> wrote:

> Dear Mohnish:
> I have used the 'vc-relax' process optimized the cell parameter, however,
> the result were seem to deviate from the initial value (experimental value)
> too much.The aim of the structure optimizes is for calculating the Raman
> spectra of the structure, I think the bad structure ( not coincide to the
> experiment) is hard to got the true spectra. So I don't how to deal with the
> case. According to your experience, what should I do for the next step?
>
> Thank you, dear Mohnish, for your kind help.
>
>
>
> 2010/9/20 mohnish pandey <mohnish.iitk at gmail.com>
>
> Dear Wang,
>>                     The 'relax' process optimizes the  structure within
>> given geometric constraint. It does'nt care for stress. It minimizes force
>> only in the given constraint. If you want to minimize the stress also you
>> have to do 'vc-relax' calculation, It will give you what you want.
>>
>> On Mon, Sep 20, 2010 at 11:37 AM, Wang Di <didi5158 at gmail.com> wrote:
>>
>>> Dear all
>>>
>>> I perform the relax calculate to the crystal structure. After 11 step
>>> bfgs,  the total force and total scf correction had reach to the criterion,
>>> however, the total stress was so big P=-3443.87. I have no idea about deal
>>> with the case,  could anyone give some advices? Thanks in advance.
>>>
>>> the input file
>>> : &CONTROL
>>>                  calculation = 'scf' ,
>>>                 restart_mode = 'from_scratch' ,
>>>                   wf_collect = .true. ,
>>>                       outdir = '/lustre/AIOFM/gxgu/workLCAF/5/temp/' ,
>>>                       wfcdir = '/lustre/AIOFM/gxgu/workLCAF/5/wftemp/' ,
>>>                   pseudo_dir = '/home/AIOFM/gxgu/work/NCPP/' ,
>>>                       prefix = 'LCAF' ,
>>>                etot_conv_thr = 1.0D-7 ,
>>>                forc_conv_thr = 1.0D-6 ,
>>>                        nstep = 100 ,
>>>                      tstress = .true. ,
>>>                      tprnfor = .true. ,
>>>                     dipfield = .true. ,
>>>  /
>>>  &SYSTEM
>>>                        ibrav = 4,
>>>                    celldm(1) = 9.42432151,
>>>                    celldm(3) = 1.94804220,
>>>                          nat = 18,
>>>                         ntyp = 4,
>>>                      ecutwfc = 30 ,
>>>                      ecutrho = 120 ,
>>>                        nosym = .false. ,
>>>  /
>>>  &ELECTRONS
>>>             electron_maxstep = 100,
>>>                     conv_thr = 1.0D-10 ,
>>>  /
>>> ATOMIC_SPECIES
>>>    Li    6.94100  03-Li.LDA.fhi.UPF
>>>    Al   26.98154  13-Al.LDA.fhi.UPF
>>>    Ca   40.07800  20-Ca.LDA.fhi.UPF
>>>     F   18.99840  09-F.LDA.fhi.UPF
>>> ATOMIC_POSITIONS crystal
>>>    Li      0.333333333    0.666666667    0.250000000
>>>    Li     -0.333333333   -0.666666667   -0.250000000
>>>     F      0.389997       0.045970       0.148326
>>>     F     -0.045970       0.344027       0.148326
>>>     F     -0.344027      -0.389997       0.148326
>>>     F     -0.045970      -0.389997       0.351674
>>>     F     -0.344027       0.045970       0.351674
>>>     F      0.389997       0.344027       0.351674
>>>     F     -0.389997      -0.045970      -0.148326
>>>     F      0.045970      -0.344027      -0.148326
>>>     F      0.344027       0.389997      -0.148326
>>>     F      0.045970       0.389997       0.648326
>>>     F      0.344027      -0.045970       0.648326
>>>     F     -0.389997      -0.344027       0.648326
>>>    Al      0.666666667    0.333333333    0.250000000
>>>    Al     -0.666666667   -0.333333333   -0.250000000
>>>    Ca      0.000000000    0.000000000    0.000000000
>>>    Ca      0.000000000    0.000000000    0.500000000
>>> K_POINTS automatic
>>>   16 16 16   0 0 0
>>>
>>> best regart
>>>
>>> Wang Di
>>>
>>> --
>>> -----------------------------------------------------------------
>>> *Wang Di**
>>> The Crystal Lab,*
>>> *AnHui Institute of Optics and Fine Mechanics, ***
>>> *Chinese Academy of Sciences,**
>>> No350. , Shushanhu Road, Hefei, 230031, China**,
>>> E-mail: didi5158 @gmail.ocm** ,*
>>> -----------------------------------------------------------------
>>>
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>>>
>>
>>
>> --
>> Regards,
>> MOHNISH,
>> -----------------------------------------------------------------
>> Mohnish Pandey
>> Y6927262,5th Year dual degree student,
>> Department of Chemical Engineering,
>> IIT KANPUR, UP, INDIA
>> +919235721300
>> -----------------------------------------------------------------
>>
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>>
>
>
> --
> -----------------------------------------------------------------
> *Wang Di**
> The Crystal Lab,*
> *AnHui Institute of Optics and Fine Mechanics, ***
> *Chinese Academy of Sciences,**
> No350. , Shushanhu Road, Hefei, 230031, China**,
> E-mail: didi5158 @gmail.ocm** ,*
> -----------------------------------------------------------------
>
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>


-- 
____________________________________
Hui Wang
School of physics, Fudan University, Shanghai, China
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