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

Hello Enrico,

I got it to work by specifying all the atoms and Abinit recognizes the symmetry group. The only thing you have to pay attention is to list the reduced coordinates in fcc lattice. You had yours in cubic lattice. I agree that most references list the coordinates in cubic lattice and you have to work to put them in fcc, but you get a small unit cell. 

To go from the reduced coordinates in the cubic lattice to the fcc lattice, you need to multiply by the inverse matrix of the fcc lattice vectors:

-1 1 1

1 -1 1

1 1 -1

I was not able to get Abinit to work using the spgroup keyword with fcc lattice. It will work with cubic lattice but then the unit cell is 4 times too large. I am not sure it this is the desire result or a problem with the geometry builder.

I copy below the input that works. Make sure that the output structure is really what you want. I did not check the other parameters of your input file.

Michel

#UNIT CELL 

LaNi2

acell  3*7.387 Angstr

rprim  0.0  0.5  0.5   # Real space PRIMitive translations fcc

       0.5  0.0  0.5 

       0.5  0.5  0.0

#spgroup 227 # without space group the spcgrp is not identified

ntypat 2 # 2 types of atoms

znucl  57 28

natom  6 # atom per cell

#natrd 2

typat 1 1 2 2 2 2 # LaNi2

xred

#internatinal table of crystallography origin -3m

1/8 1/8 1/8 # 8a wyckoff position 

#7/8 3/8 3/8

-1/8 -1/8 -1/8

1/2 1/2 1/2 # 16d

#1/2 1/4 1/4

0 1/2 1/2

#1/4 1/2 1/4

1/2 0 1/2

#1/4 1/4 1/2

1/2 1/2 0

Le 08-04-16 à 06:39, Enrico Avenati a écrit :

I tried in this case you should also change 

natom  24 # atom per cell

but i got always the same error. 
i'm using abinit 5.3.4, i don't  think it matter but...
thank you in advance

----- Original Message ----
From: Michel Cote <Michel.Cote@umontreal.ca>
To: forum@abinit.org
Sent: Wednesday, April 16, 2008 3:21:42 PM
Subject: Re: [abinit-forum] Geometry LaNi2

Try to specify only the non-equivalent atoms:

spgroup 227 # without space group the spcgrp is not identified

ntypat 2 # 2 types of atoms

znucl  57 28

natom  6 # atom per cell
natrd 2
typat  1 2

xred

#internatinal table of crystallography origin -3m
1/8 1/8 1/8 # 8a wyckoff position
#7/8 3/8 3/8
1/2 1/2 1/2 # 16d
#1/2 1/4 1/4
#1/4 1/2 1/4
#1/4 1/4 1/2

---

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_____________________________________

Michel Cote

Departement de physique

Universite de Montreal

email: Michel.Cote@umontreal.ca

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