[Pw_forum] using ev.x

[udayagiri sai babu]

Dear stefano baroni
I tried that as well i am getting the same value (255gpa). This is the data
i am using

5.35    -174.156857800
5.36    -174.156934850
5.37    -174.156989300
5.38    -174.156990580
5.39    -174.156955990
5.4    -174.156869280

this is one of the input file

 &control
calculation = 'scf',
restart_mode='from_scratch',
outdir='/home/sai/temp',
prefix='chromium'
pseudo_dir='/home/sai/softwares/espresso-4.0.1/pseudo/',
tstress = .TRUE.,
tprnfor = .TRUE.,
/
&system
ibrav=3
celldm(1)=5.350000,
nat=1,
ntyp=1
ecutwfc=30,
ecutrho=300,
occupations='smearing',
smearing='mv',
degauss=0.012000
/
&electrons
conv_thr=1.D-8,
diagonalization='david',
mixing_mode='plain',
mixing_beta= 0.7
/
ATOMIC_SPECIES
Cr  51.9961  Cr.pw91-sp-van.UPF
ATOMIC_POSITIONS (crystal)
Cr     0.00000000    0.00000000    0.00000000
K_POINTS {automatic}
12 12 12 0 0 0

can you suggest me anything

On Wed, Sep 9, 2009 at 1:03 AM, Stefano Baroni <baroni at sissa.it> wrote:

> How about trying to fit a very accurate set of data around the minimum with
> a parabola and calculate thus the bulk modulus? Have you tries to plot the
> resulting fitted curves? which one fits best the raw data? Udaygiri: in
> Science (as well as in Life) there is no free lunch ... Enjoy Science, no
> less than Life. SB
> On Sep 8, 2009, at 9:04 PM, udayagiri sai babu wrote:
>
>
> hi all
> i am using ev.x file given in the pw_tools directory to calculate bulk
> modulus and lattice parameter values of chromium. i used murnaghan equation
> of state to fit my data i got bulk modulus of 256 gpa where as my
> experimental  value is 160 gpa but when i used keane equation of state to
> fit the same data i got 148 gpa bulk modulus
>
> why is this much variation? which equation of state should i use for cr?
> because for vanadium and Ti murnagan euation of state has given reasonable
> (<20% error) values of bulk modulus but not for Cr
>
> please give some suggestions
> --
> U.Saibabu
> PhD student,
> Deformation mechanisms modeling group,
> Materials engineering department,
> IISc Bangalore,
> India.
>
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>
> ---
> Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
> http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) /
> stefanobaroni (skype)
>
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>
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-- 
U.Saibabu
PhD student,
Deformation mechanisms modeling group,
Materials engineering department,
IISc Bangalore,
India.
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