[Pw_forum] Error 254 (fwd)

[Axel Kohlmeyer]

resent to pw_forum without attachments, to avoid
spamming everybody's mailbox with 2 megabytes of data,
they (probably) don't need. ;-)

a.

---------- Forwarded message ----------
Date: Fri, 31 Dec 2004 16:51:45 +0100 (CET)
From: Axel Kohlmeyer <axel.kohlmeyer at theochem.ruhr-uni-bochum.de>
To: Roberto G. A. Veiga <raveiga at yahoo.com>
Subject: Re: [Pw_forum] Error 254


ok, this is one of the 'not-so-obvious to the beginner' type
of problems. you have to be aware, that celldm(...) is in 
_atomic units_ and not in angstrom. when visualizing your
start coordinates _with_ the periodic images, it is obvious,
that you have mixed that up (see the attached snapshots).
if you prefer using angstrom, you can as easily describe
your supercell by:

          ibrav = 8,  a = 16.0, b = 16.0, c =  5.40224,

and losing the CELL_PARAMETERS section.

[...]
RV>                      tefield = .false. ,
RV>  /
RV>  &SYSTEM
RV>                        ibrav = 0 ,
RV>                    celldm(1) = 16 ,
RV>                          nat = 40 ,
RV>                         ntyp = 2 ,
RV>                      ecutwfc = 200 ,
RV>                      ecutrho = 800 ,

wow, you are using a _huge_ plane wave cutoff. what type of
pseudopotentials are you using? if they are norm-conserving
troullier-martins pseudopotentials, you can probably get away
with something between 50 and 100 ry, if they are ultrasoft
pseudopotentials you should get good results with 20-30 ry.

i've attached a set of vanderbilt uspps that should work
very well with ecutwfc = 25.0 and  ecutrho = 150.0.

considering the size and the nature of your system, you
should check, whether you need to use more k-points (at least
in z-direction) and/or smearing.

best regards,
	axel.

-- 

=======================================================================
Dr. Axel Kohlmeyer   e-mail: axel.kohlmeyer at theochem.ruhr-uni-bochum.de
Lehrstuhl fuer Theoretische Chemie          Phone: ++49 (0)234/32-26673
Ruhr-Universitaet Bochum - NC 03/53         Fax:   ++49 (0)234/32-14045
D-44780 Bochum  http://www.theochem.ruhr-uni-bochum.de/~axel.kohlmeyer/
=======================================================================
If you make something idiot-proof, the universe creates a better idiot.