The ABINIT Users Mailing List ( CLOSED )

["Josef W. Zwanziger" <jzwanzig@dal.ca>]

Dear Colleagues,

I'm a little confused about what ecutsm does. The explanation in the
help file seems clear enough, but I find the following behavior.
Starting from an experimentally determined crystal structure, I optimize
the atom positions and unit cell dimensions with

ionmov 2
ntime 200
tolmxf 2.0D-5
toldff 2.0D-6

optcell 2
dilatmx 1.1
ecutsm 0.5

This procedure seems to work fine--the crystal structure changes
slightly, with the result that the stress tensor calculated for the
final structure has elements of order 10-8 H/Bohr^3. Then if I take the
output structure (new acell values, new xred values, rprim didn't change
of course) and compute the energy with toldff 2.0D-6, but no ecutsm, the
computed stress tensor rises to nearly 10-5 H/Bohr^3. If I then put back
in the ecutsm 0.5 line, the stress tensor goes back down. Can someone
shed some light on this? I already have ecut set rather high (70 H) and
am using 4x4x4 M-P grid with shiftk 0.5 0.5 0.5. 

Thanks much for your help,

Joe

Josef W. Zwanziger             tel: (902) 494-1960
Professor of Chemistry and     fax: (902) 494-1867
  Canada Research Chair in     net: jzwanzig@dal.ca
  NMR Studies of Materials     web: http://jwz.chem.dal.ca
Dept. of Chemistry
Dalhousie University
Halifax, NS 
B3H 4J3 CANADA