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

[Lyudmila Dobysheva]

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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