[Pw_forum] vc-relax with PW
Konstantin Kudin
konstantin_kudin at yahoo.com
Fri Jan 19 06:02:33 CET 2007
Hi all,
This is a public announcement coupled with a request for qualified
help, so if you are NOT interested, please disregard.
I added some constraints on cell coordinates for vc-relax to the CVS,
so that one can optimize only a subset of those.
Here is an example of cell_dynamics='damp-w' :
input lattice vectors (alat, hexagonal cell, vacuum in Z)
1.000000 0.000000 0.000000
-0.500000 0.866025 0.000000
0.000000 0.000000 1.250000
first step stress:
total stress (Ry/bohr**3) (kbar) P=
-15.58
0.00066135 0.00012844 0.00000009 97.29 18.89
0.01
0.00012844 -0.00097768 -0.00000005 18.89 -143.82
-0.01
0.00000009 -0.00000005 -0.00000129 0.01 -0.01
-0.19
The old code would update to:
1.000003703 0.000000719 0.000000001
-0.500001229 0.866019900 0.000000000
0.000000001 0.000000000 1.249999991
The new code with constraints can do this:
1.000003703 0.000000000 0.000000000
-0.500000614 0.866019900 0.000000000
0.000000000 0.000000000 1.250000000
So only x1, x2, and y2 are updated.
What is interesting is that it looks like the fully unconstrained code
is somewhat rotating the lattice vectors (note the +delta_y1 and
-delta_x2).
If somebody understands what the VC code actually does, please take a
look.
Kostya
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