[Pw_forum] question about the stress in relax process

[Wang Di]

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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