[Wien] what's the difference between the fitting Murnaghan’s equation of state and the minimizing total energy method?

[Stefaan Cottenier]

There is of course no difference in principle, just in practice. By  
calculating the total energy for say 7 volumes (a set that does not  
need to include the exact minimum) and by fitting it by an equation  
that is built to contain the right type of shape of the E(V) curve,  
you fit (=interpolate) the value of the minimum. You can do it of  
course as well by making many many total energy calculations with a  
small step in volume, but it will take much more time and you will see  
small numerical fluctuations of the energies that will make it hard to  
decide where (with this fine step size) the minimum *really* is.

Stefaan


> Dear Wien2k users,
>
> I determined the lattice constant via WIEN2K code. According to the
> userguide  I calculated the total energy as a function of lattice constant
> by varying the supercell volume isotropically. Then, around the region of
> the total energy minimum, the equilibrium lattice constants were fitting the
> data to Murnaghan’s equation of state. Is it true that the  equilibrium
> lattice constants are obtained by fitting the data to Murnaghan’s equation
> of state instead of  by the minimizing total energy method? If so, is there
> any difference between them? Thanks a lot.
> With best regards,
>
> He Duan, PhD
> Room 24309, National Laboratory for Infrared Physics
> Institute of Technical Physics
> Chinese Academy of Sciences
> 500 Yutian Road
> Shanghai, 200083, China
> E-mail: duanhe at mail.sitp.ac.cn
>
>                                                               Nov 12, 2006
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>



-- 
Stefaan Cottenier
Instituut voor Kern- en Stralingsfysica
K.U.Leuven
Celestijnenlaan 200 D
B-3001 Leuven (Belgium)

tel: + 32 16 32 71 45
fax: + 32 16 32 79 85
e-mail: stefaan.cottenier at fys.kuleuven.be


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