[Pw_forum] Etot in cp.x vs pw.x

[sylvian kahane]

Regarding the response of  Lorenzo Paulatto

You are right on both accounts. The calculations involved 54 atoms of Li.
For the cp.x I used Vanderbild uspp with 1 valence electron
and for the pw.x, a paw calculated with Holzwarth program with all 3
electrons as valence.

When I am looking in the literature Jarlborg (Physica Scripta 37, 795
(1988)) gives -14.84 Ry/atom and this is what I got in my pw calculation
-800/54=-14.81, but  Dacorogna and Cohen (Phys. Rev. B 34, 4996 (1986) gave
-0.617 Ry/atom, which is not close but resembles my result from cp.x
-47*2/54=-1.74 Ry/atom.

Why I am bothered by these values ? I got involved in some EOS calculations
and I am trying to solve what is called as first shock
Hugoniot equation (which takes you from an initial state P1, V1, U1
(pressure, volume, internal energy) to a final state P2, T2, U2 by a shock):

                                 (U2 - U1) = 1/2*(P1+P2)*(V2-V1)   if
I remember correctly

in which you have to put the initial values.  For U I use

                                 U=3/2kT + Etot/N (N=54)

following some papers by one Lenosky (I don't have references right here).
So, if in this equation you use -1.74 Ry or -14.8 Ry it makes a hell of a
difference.

-- 
Sylvian (gmail:  sylviankahane at gmail.com)
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