[Wien] optimize & mini for crystal lattice

[J. M. Rondinelli]

One simple approach would be to fit your results (energy w/r/t volume) using
the Murnaghan equation. It is given as:

E(V) = E_0 + (B_0 * V) / B1_0 * ( (V_0/V)^B1_0 / (B1_0 - 1) + 1 ) -
           -  B_0 * V_0 / (B1_0 - 1)

There are 4 parameters
a0 = E_0 - B_0 * V_0 /  (B1_0 - 1)
a1 = B_0
a2 = B1_0
a3 = V_0

So the fitting equation (using xmgrace for instance) is:

y = a0 + (a1*x)/a2 * ((a3/x)^a2 / (a2-1) + 1)

where x is the volume in atomic units (bohr^3), and y is the energy in
Hartree units. After the fit, a3 is the equilibrium volume (so take the
cubic root to have a_0), and a1 is the bulk modulus B_0 in atomic units. How
to convert atomic units to human units?

a_0 [Ang] = a_0 [bohr] * 0.529177
B_0 [GPa] = B_0 [a.u.] * 2.9421 * 10^4




----------------------------------------
James M Rondinelli
Materials Department
University of California, Santa Barbara
Santa Barbara, CA 93106-5050  USA
Tel: (805) 893-7934  Fax: (805) 893-8502
Office: MRL 2236
Email: rondinelli.at.umail.ucsb.edu 
----------------------------------------
-----Original Message-----
From: wien-bounces at zeus.theochem.tuwien.ac.at
[mailto:wien-bounces at zeus.theochem.tuwien.ac.at] On Behalf Of ???
Sent: Tuesday, August 29, 2006 18:34
To: wien at zeus.theochem.tuwien.ac.at
Subject: [Wien] optimize & mini for crystal lattice

Dear all,
     I am glad to communicate with you ! Recently, I am performing the
calculation on the optimization of crystal lattice & the relaxation
of atomic positions. I had selected a series of volumes of crystal
and run the commands "optimize" & "mini". In the file optimize.job, I
adopted  the min -I -j "run_lapw -I -fc 1.0 -i 200 -p" and the file
as:

>#!/bin/csh -f
>#   Modify this script according to your needs:
>#      Uncomment one of the lines ...
>#      Change run_lapw to runsp_lapw or use different convergence criterium
>#      Change save_lapw -d XXX
>foreach i ( \
>                                         Bi2O3_abc___1.0  \
>                                         Bi2O3_abc___2.0  \
>                                         Bi2O3_abc___3.0  \
>                                         Bi2O3_abc___4.0  \
>                                         Bi2O3_abc___5.0  \
>                                         Bi2O3_abc___6.0  \
>                                         Bi2O3_abc___7.0  \
>                                         Bi2O3_abc___8.0  \
>                                         Bi2O3_abc___9.0  \
>                                         Bi2O3_abc__10.0  \
> )
>     cp  $i.struct Bi2O3.struct

> # Please uncomment and adapt any of the lines below according to your
needs
> #    cp  $i.clmsum Bi2O3.clmsum
> #    x dstart
> #    x dstart -c
> #    run_lapw -ec 0.0001 -in1new 3 -in1orig -renorm
> #    runsp_lapw -ec 0.0001
>      min -I -j "run_lapw -I -fc 1.0 -i 200 -p"
> #    run_lapw -ec 0.0001

>     set stat = $status
>     if ($stat) then
>        echo "ERROR status in" $i
>        exit 1
>     endif
>     save_lapw  $i
> #    save_lapw  -f -d XXX $i
> end

    Now, the question is how to analyze the calculated results. That is
how to determine the equilibrium volume. Am I select the volume of
minimum total energy from these 10 volumes?
     Thanks for any help!

Best Wishes!

-- 
=====================================================
Mr. GuoHua Zhong
Address:
    Key Laboratory of Materials Physics,Institute
    of Solid State Physics, Chinese Academy of Sciences
    Hefei, Anhui P.O.Box 1129, 230031 P. R. China
Telephone:
    86-551-5591464 (Office)
E-Mail:
    zhgh at theory.issp.ac.cn



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