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[Michel Cote <Michel.Cote@umontreal.ca>]

Hello Genesh,

I think Abinit does not recognize the cubic Fm-3m structure (#225) because your input describe a tetragonal structure (#25). Abinit symmetry subroutine cannot reduce the given unit cell to find the "optimal" unit cell. Probably FINDSYM can do that. If you want to simulate the Fm-3m structure, you will have to input the cubic cell.

Michel Côté

Le 07-10-22 à 08:02, P. Ganesh a écrit :

The values for the 3rd and 4th atom are:

0.0 0.0 0.00

0.0 0.0 0.50

Sorry about the misprint in my email (I was also trying for tetragonal distortions as well and hence the mixup).  But the problem remains the same.  ABINIT does not recognise the now corrected coordinates to be Fm-3m (or recognise it to be I4mm with the distortion of 0.01 in reduced coordinates of the 3rd and 4th atom as entered below).   Findsym recognises them to be so if I select them to be I centered.

Thanks,

Ganesh

Xavier Gonze wrote:

Dear Ganesh,

The input below is definitely NOT Fm-3m.

One does not need a computer code to see this ... atoms 3 and 4 are NOT at a symmetric position.

You must have given another input to FINDSYM ?!

Or perhaps you have given a tolerance of more than one percent to FINDSYM ?!?

Xavier

On 21 Oct 2007, at 20:43, P. Ganesh wrote:

I am having trouble with getting ABINIT to give the right space group!!

For example,  if I give the coordinates (listed below) into the "FINDSYM" program (it is known to be a reliable source to find symmetries.  one can google it) and select 'I' centering I get the correct space-group I want (since I worked out the co-ords.), Fm-3m (#225).  But ABINIT finds the spacegroup to be Pmm2 (#25) . So why doens't ABINIT recognise the spcgrp. to be #225 ?  Do I need to shift the origin to get the centering correct? I am not using any symmetry variable, system is non-magnetic.

Thank you in advance for any suggestions.

Ganesh

typat 1 2 3 3 4 4 4 4 4 4

acell     7.09 7.09 14.18

rprim     1.0 -1.0 0.0

         1.0 1.0 0.0

         0.0 0.0 1.0

xred      0.0 0.5 0.25

         0.0 0.5 0.75

         0.0 0.0 0.01

         0.0 0.0 0.51

         0.25 0.25 0.0

         -0.25 0.25 0.0

         0.0 0.0 0.25

         0.25 0.25 0.5

         -0.25 0.25 0.5

         0.0 0.0 0.75

_____________________________________

Michel Cote

Departement de physique

Universite de Montreal

emai: Michel.Cote@umontreal.ca

web: http://www.phys.umontreal.ca/~michel_cote