[Pw_forum] very high pressure in scf

[Stefano de Gironcoli]

I think the two structures are not the same, or some of the parameters 
have non equivalent
values.
stefano

On 05/26/2011 08:50 PM, Sanjeev Gupta wrote:
> Dear Sir,
> Thanks for reply.
>
>
> On Thu, May 26, 2011 at 10:23 PM, Stefano de Gironcoli<degironc at sissa.it>wrote:
>
>>   with this input the Fe-N distance is some 1.2 A... I'm pretty sure it
>> cannot be the intended structure
>> Are you sure the system is not in crystal coordinate ?
>>   stefano
>>
> Yes, its true that  while looking from xcrysden particularly the bond
> lengths between the Fe-N and N-N  but i am very surprised why both ABINIT
> and PWSCF code gives such vast Difference in calculated Pressure for the
> identical geometry which is not cleared yet. Here the bond lenth Fe-N is
> ~1.24Ang.
> Please Suggest More.
>
>
>
>> On 05/26/2011 04:13 PM, Sanjeev Gupta wrote:
>>
>> Dear Maxim
>>
>> Thank for kind reply.
>>
>> My unit cell is as same in ABINIT  as in pwscf in Bohr  unit. In addition I
>> am using the spacegroup 166   (R3(bar)M) space group with conventional unit
>> cell rather than primitive unit cell the lattice parameter is taken as below
>> 1. for abinit
>>
>> a=5.359168252 Bohr
>> b=5.359168252 Bohr
>> c=20.08294707 Bohr
>>
>> 2. for PWSCF
>>
>> ibrav=4,
>> celldm(1) = 5.359168242 Bohr
>> celldm(3) = 3.7474
>>
>> Part of my input file is :
>>
>> PWSCF
>>
>> &control
>>      calculation = 'scf'
>>      prefix='FeN2',
>>      restart_mode='from_scratch',
>>      outdir='./'
>>      pseudo_dir = '/',
>>      tstress = .true.
>>      tprnfor = .true.
>>      etot_conv_thr = 1.0d-5,
>>      forc_conv_thr = 1.0d-4,
>>   /
>>   &system
>>      ibrav=4,
>>      celldm(1) = 5.359168242,
>>      celldm(3) = 3.7474
>>      nat=9,
>>      ntyp=2,
>>      nosym =.true.,
>>      ecutwfc = 20,
>>      ecutrho=200,
>>      occupations='smearing',
>>      smearing='m-p',
>>      degauss=0.001,
>>   /
>>   &electrons
>>       mixing_mode     = "local-TF",
>>       mixing_beta     =  0.700000,
>>       conv_thr        =  1.0d-10,
>> /
>> ATOMIC_SPECIES
>> Fe  55.845  Fe.pbe-sp-van.UPF
>> N   14.0067 N.pbe-van_ak.UPF
>> ATOMIC_POSITIONS
>> Fe    -1.8503717077E-17 -1.8503717077E-17 -1.8503717077E-17
>> N     -1.8503717077E-17 -1.8503717077E-17  4.4000000000E-01
>>
>> ..........................................
>>
>> N      3.3333333333E-01  6.6666666667E-01  2.2666666667E-01
>> K_POINTS automatic
>> 6 6 6 0 0 0
>>
>>
>> Best Regards
>>
>>
>> Sanjay D. Gupta
>> Research Fellow
>> Department of Physics,
>> Bhavnagar University, Bhavnagar-364 022
>> Gujarat, Mobile-9879666643email:guptasanjay_56 at yahoo.co.in
>>
>>
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