[Pw_forum] problem in vc-relax

[vkarthik]

ATOMIC_POSITIONS {crystal}
C        0.00  0.00 0.00
Mo       0.3333333   0.666666   0.25
Mo       0.6666666   0.333333   0.75

This will work for hexagonal system.

Quoting "Arles V. Gil Rebaza" <arvifis at gmail.com>:

> Hi Ashish Kumar, if you don't know: vc-relax means variable-cell relax. So,
> you're doing this kind of calculation, where the default is relax all cell
> parameters ( axis, angles, position). You can choose which parameters are
> fixed or which parameters are relaxed, please read the QE manual, the
> section  &CELL , the variable "cell_dofree"
>
> Best.
>
> PhD stud Arles V. Gil Rebaza
> IFLP - Argentina
>
> 2011/10/4 Ashish Kumar <ashishespresso at gmail.com>
>
>> Hello to all,
>>
>> I have tried for the vc-relax of Mo2C hexagonal system, job is not done
>> properly it come out in between and the atomic positions
>>
>> what I have given in the input file and what I am getting in the out file
>> is different.
>> (i) Why the crystal positions changes. what I think that the nature of the
>> atomic postions must be retained.
>>
>> In Input file
>> ATOMIC_POSITIONS (alat)
>> C        0.00  0.00 0.00
>> Mo       0.3333333   0.666666   0.25
>> Mo       0.6666666   0.333333   0.75
>>
>>
>>
>> In out file we get
>>
>> CELL_PARAMETERS (alat=  5.67296009)
>>    0.946518633   0.001215132  -0.004855406
>>   -0.474470641   0.819090796  -0.000958606
>>    0.009278926   0.007480907   1.741942673
>>
>> ATOMIC_POSITIONS (alat)
>> C        0.156590059   0.041446237  -0.212516996
>> Mo       0.157761886   0.589915381   0.269109338
>> Mo       0.636664528   0.321113609   1.041609035
>>
>>
>>
>>
>> (ii) why cell_parameter changes in the out file . (I think that for
>> hexagonal system it must be what given in the input file)
>>
>>
>> my input file
>>
>> &control
>>     calculation='vc-relax'
>>     restart_mode='from_scratch',
>>     pseudo_dir = '/home/ashish/softwares/espresso/pseudo/',
>>     outdir='/home/ashish/dft/espresso_mo2c/test1/tmp_espresso/'
>>     prefix='mo2c'
>>     tprnfor = .true.,
>>     tstress = .true.
>>  /
>>  &system
>>     ibrav=4, celldm(1) =5.672960087 , celldm(3)=1.573617588 , nat=3,
>> ntyp=2,
>>     nspin = 1,  starting_magnetization(1)=0.7,
>>     ecutwfc = 24.0, ecutrho = 288.0,
>>     occupations='smearing', smearing='methfessel-paxton', degauss=0.02
>>  /
>>  &electrons
>>     diagonalization='cg'
>>     conv_thr = 1.0e-8
>>     mixing_beta = 0.7
>> /
>> &ions
>>   ion_dynamics='bfgs'
>>  /
>> &cell
>> cell_dynamics='bfgs'
>> /
>> ATOMIC_SPECIES {crystal}
>>  C  12.01 C.pw91-van_ak.UPF
>>  Mo 95.94 Mo.pw91-n-van.UPF
>> ATOMIC_POSITIONS
>>  C 0.0 0.0 0.0
>>  Mo 1/3 2/3 1/4
>>  Mo 2/3 1/3 3/4
>>
>> K_POINTS automatic
>>  4 4 4   0 0 0
>>
>>
>>  can any one help me. What is the mistake (in my input file or else)
>>
>>
>> with best wishes
>> Ashish
>>
>>
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>>
>>
>
>
> --
> ###--------->   Arles V.   <---------###
>