The ABINIT Users Mailing List ( CLOSED )

["matthieu verstraete" <matthieu.jean.verstraete@gmail.com>]

If your initial structure is BCC, just set

ionmov 2 # BFGS relaxation
optcell 2 # full relaxation of the cell
dilatmx 1.05
tolmxf 1.e-5
ecutsm 0.5
ntime 20

and run! The symmetries will ensure that the system stays bcc. If you want to do it by hand, just vary acell and keep rprim fixed. The factor of 2 you add is probably wrong. Need to check the real lattice vectors you get inside the abinit run. The formula you were given describes how the lattice (rprimd - d for dimensionful or dimensional, ie in Bohr) is calcuated from rprim (dimensionless a priori) and acell
rprimd(:,i) = rprim(:,i) * acell(i) for i=1,2,3

The factor of 2 idea probably comes from the fact that if you use the cubic FCC lattice parameter for acell and want the primitive (1 atom) unit cell, you need to set something like:
rprim
0     0.5   0.5
0.5  0      0.5
0.5   0.5  0

to get the right rprimd.

Cheers

Matthieu

On Mon, Nov 10, 2008 at 10:03 AM, Enrico Avenati <enrico.avenati@yahoo.com> wrote:

I'm found an error in my calculation!
That's why i got such an impressive energy difference!
Anyways the compound should not be stable according to TM psp. I'm checking with other rare erath!

Instead this quetsion is still open for

2) i would like to know how i should manage the RPRIM variation in BCC
structure to find ACELL parameters.

I've notice it changed from 0.5 to 0.57xx.

Should i do as for the FCC? = 2 * rprim*acell ( as I was suggetsted)

THANK YOU
                         Enrico

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-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF) 
Dpto. Fisica de Materiales, 
U. del Pais Vasco,            
Centro Joxe Mari Korta, Av. de Tolosa, 72,   Phone: +34-943018393
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Mail : matthieu.jean.verstraete@gmail.com
http://www-users.york.ac.uk/~mjv500