[Pw_forum] using ev.x

[Stefano de Gironcoli]

Dear Saibabu,

  using your data with ev.x I obtain very similar results using birch 1 
& 2 and murnaghan EoS while very different when using keane EoS... this 
indicates that keane EoS has met some problem (at least with your data...)
  I notice that your data points span less than 1% around the 
equilibrium geometry. Usually one takes a larger range (let's say 5-10 
%) which reduces the signal/noise ratio.
 hope this helps
  stefano de Gironcoli - SISSA and DEMOCRITOS

udayagiri sai babu wrote:
> 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 
> <mailto: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)
>
>     La morale est une logique de l'action comme la logique est une
>     morale de la pensée - Jean Piaget
>
>     Please, if possible, don't  send me MS Word or PowerPoint attachments
>     Why? See:  http://www.gnu.org/philosophy/no-word-attachments.html
>
>
>
>
>
>
>
>
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>
>
> -- 
> U.Saibabu
> PhD student,
> Deformation mechanisms modeling group,
> Materials engineering department,
> IISc Bangalore,
> India.
>
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