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[matthieu verstraete <matthieu.jean.verstraete@gmail.com>]

And last but not least you can also use xmgrace, which does a least
squares fit to any function you give it:

* load your data E(V) (I presume below you use atomic Hartree for
everything, otherwise you will have a hard time with units)

* go to menus Data->Transformations->Non-linear curve fitting

* set the number of parameters to 4 (E_min, B0, B', and V_min in that order)

* enter the following (for Murnaghan EOS) in the Formula: y =
A0 + (A1*x)/(A2*A2-A2)  *  (  A2*(1.-A3/x) + exp(ln(A3/x)*A2)-1.  )

* you may also have to set some reasonable starting values, eg
 A0,1,2,3 = typical etot,  0.001,  4, typical volume
otherwise it may not converge (due to the sensitive dependency on the power 
A2)

* hit Apply (eventually several times if 5 iterations of least-squares
convergence is not enough)

* read off converged values of parameters:
A1* 2.9421e+04 is B_0 in GPa
A2 = B' is unitless

* you can also extract the equilibrium energy and volume by hand and
fit with only 2 parameters (I find this works better sometimes).



Matthieu


On Thu, Sep 24, 2009 at 10:19 AM, Marcin Dulak
<Marcin_Dulak@poczta.onet.pl> wrote:
> Hi,
>
> there is also a python tool:
> https://svn.fysik.dtu.dk/projects/CamposASE2/trunk/ASE/Utilities/EquationOfState.py
> a part of ASE
> https://wiki.fysik.dtu.dk/ase2/Utilities?highlight=(equation)#the-equationofstate-module
>
> Best regards,
>
> Marcin
>
> Igor Lukacevic wrote:
>>
>> Thank you all for your replies! I'll try your proposals. You've been more
>> than helpful.
>>
>> Cheers!
>>
>> Igor Lukacevic
>>
>> On Wednesday 23 September 2009 17:44, Scott Beckman wrote:
>>
>>>
>>> You can fit the Birch-Murnaghan equation of state using steepest
>>> decent (and LOTS of patience) or the conjugate gradient method.  (I
>>> also did this in Mathematica.)
>>>
>>> Alternatively you can download Quantum-Espresso and use the ev.f90
>>> fitting program that is in the pwtools subdirectory.
>>>
>>> It's more fun to write your own software, but if you don't have time
>>> it is best to search all of the major DFT/LDA software developers
>>> since it has probably been implements in at least one of them.
>>>
>>> On Sep 23, 2009, at 10:11 AM, Igor Lukacevic wrote:
>>>
>>>>
>>>> Dear all,
>>>>
>>>> please, share with me your experience in fitting E(V) curves with
>>>> Birch-Murnaghan equation of state. Which sofware do you usually
>>>> use? I tried
>>>> with Mathematica, but I fail to reproduce the B_0 correctly (other
>>>> 3 factors
>>>> are ok).
>>>> Anything is wellcome.
>>>>
>>>> Thank you in advance!
>>>>
>>>> Igor Lukacevic
>>>> --
>>>> Igor Lukacevic
>>>> Department of Physics
>>>> University of J. J. Strossmayer
>>>> Trg Ljudevita Gaja 6
>>>> 31000 Osijek
>>>> Croatia
>>>>
>>
>>
>
>



-- 
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Prof. Matthieu Verstraete

Universite de Liège
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Mail : matthieu.jean.verstraete@gmail.com