[Wien] Vol optimization for BaRuO3, propose to change eosfit
delamora
delamora at unam.mx
Fri Feb 27 17:22:21 CET 2015
Thanks Peter, Victor and Lyudmila,
From Peter Blaha's suggestion I extended the Vol range to the right 'negative' pressures and I was able to fit the points.
Pablo
________________________________________
De: wien-bounces at zeus.theochem.tuwien.ac.at <wien-bounces at zeus.theochem.tuwien.ac.at> en nombre de Peter Blaha <pblaha at theochem.tuwien.ac.at>
Enviado: viernes, 27 de febrero de 2015 09:58 a. m.
Para: A Mailing list for WIEN2k users
Asunto: Re: [Wien] Vol optimization for BaRuO3, propose to change eosfit
Thank you very much for your improvements.
I agree that better starting values will help the fit and thus take your
suggestions for Murnaghan and Birch-Murnaghan.
However, for EOS2, the values of "x" have nothing to do with E0, V0, B,
BP and thus using your starting values may be good in one case, but not
good in others.
For instance for our famous "TiC" example, the fitted values are:
Equation of state: EOS2 (PRB52,8064) info 2
a,b,c,d -1778.379016 -30.538896 -132.038868
727.308860
Even -1778.379016 is quite far from E0 ( -1783.962) and the others can
be large positive or negative in various examples.
Best regards
Peter
On 02/27/2015 10:56 AM, Lyudmila Dobysheva wrote:
> On 26.02.2015 00:28, delamora wrote:
>> Indeed there is no fit for the EOS2, Murnaghan, but for the
>> Birch-Murnaghan there is a fit.
>> V0,B(GPa),BP,E0 NaN NaN NaN
>> Equation of state: Murnaghan info 5
>> E=E0+[B*V/BP*(1/(BP-1)*(V0/V)**BP +1)-B*V0/(BP-1)]/14703.6
>> V0,B(GPa),BP,E0 NaN NaN
>> NaN NaN
>> 390.4272 -25794.173431 -0.000730 NaN NaN
>> Equation of state: Birch-Murnaghan info 5
>> E = E0 + 9/16*(B/14703.6)*V0*[(eta**2-1)**3*BP +
>> (eta**2-1)**2*(6-4*eta**2)]
>> --> eta = (V0/V)**(1/3)
>> V0,B(GPa),BP,E0 74.4783 -14614.5174 5.9286
>> -25780.948961
>
> The fit for the Birch-Murnaghan is also not good: gives bad V0, though
> on the plot it is clearly seen by eye.
> I have tried a fit of Murnaghan through simply gnuplot, and it gave
> rather good answer:
> V0= 454.289 +/- 7.335 (1.615%)
> B = 97.7233 +/- 25.87 (26.48%)
> BP= 7.63145 +/- 0.8111 (10.63%)
> E0= -25794.2 +/- 0.002309 (8.952e-06%)
>
> I checked in the eosfit a choice of starting parameters and it is really
> not good.
> In your case you have rather large scope in volume deviations, and I
> think that when initial parameters for fitting are too far from the
> minimum point it gives error. I have also met sometimes with such cases
> of unclear refuse to work.
>
> So I'd like to suggest an amendment to eosfit: it is better to take the
> minimun energy and the correspondent volume as initials.
> I am sending the changed version of the program in attachment, I think
> it should be more stable.
> The amendments suggested:
> lyu at trusty>diff eosfit.f eosfit.f-old
> 48,60c48,51
> < ! FINDING THE MINIMUM ENERGY
> < Emin=e(1)
> < kmin=1
> < do 1222 k=2,i-1
> < if (e(k).gt.Emin) goto 1222
> < Emin=e(k)
> < kmin=k
>
> < 1222 continue
> < !
> < x(1)=e(kmin)
> < x(2)=vol(kmin)
> < x(3)=100.d0
> < x(4)=5.d0
> ---
> > x(1)=e(1)
> > x(2)=1.d0
> > x(3)=-10.d0
> > x(4)=100.d0
> 103,104c94,95
> < x(1)=e(kmin)
> < x(2)=vol(kmin)
> ---
> > x(1)=emurna(3)
> > x(2)=vol(3)
> 175,176c166,167
> < x(1)=e(kmin)
> < x(2)=vol(kmin)
> ---
> > x(1)=ebm(3)
> > x(2)=vol(3)
>
> Now it gives Murnaghan:
> From gnuplot 454.289 97.7233 7.63145 -25794.2
> V0,B(GPa),BP,E0 454.2473 97.8633 7.6275 -25794.221591
> and Birch-Murnaghan:
> V0,B(GPa),BP,E0 469.9829 31.3139 27.4110 -25794.223651
>
> Best regards
> Lyudmila Dobysheva
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--
P.Blaha
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