[Wien] Vol optimization for BaRuO3, propose to change eosfit

[Peter Blaha]

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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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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