[Wien] NOSE thermostat (NAN ¬ EFG - Error)

[Peter Blaha]

Hi,

Your mail was too big for the mailing list, but since it is of general 
interest to know how to perform a MD-simulation for a metallic system, 
I'll try to answer it briefly. I've not repeated the calculations 
myself, but just a few hints:

i) Your original struct file has RMTs of 2.32, which is close to 
touching in "ideal" bcc Fe. How should this allow for a MD run, where 
atoms will come much closer to each other. The nn-distances will depend 
on temperature and my experience dates back 20 years, but a first guess 
would be to use RMTs=2.0
ii) k-mesh: You cannot do a 2x2x2 Fe cell with just one k-point. There 
is a good reason why almost nobody does MD runs for metals, because even 
when it is expensive, you need a reasonable k-mesh (a first lousy guess 
would be to use 100 k-points in the full zone)
iii) Since you want to do calculations at 1000K, you should not use 
TETRA, but TEMP 0.007   in case.in2c
iv) For a MD-run you should start with randomly displaced positions. So 
displace all your atoms a bit in some arbitrary way. Otherwise all your 
forces are ZERO, and the MD does not know how to move your atoms.
v) Fe is of course magnetic, so you have to use a spin-polarized setup 
and replace the default run_lapw -script by runsp_lapw.

PS: You may have noticed that your first
        min_lapw -j "run_lapw -I -fc 1.0 -i 40"
step stopped after 4 cycles. :ENE and :DIS was not converged at all, but 
since all forces were zero, the -fc criterium was fullfilled and the 
scf-calculation stopped.

v) Before you start   min_lapw; i'd run a normal   runsp_lapw -fc 1 to 
see how it works (and if it converges in the 40 cycles you set (I doubt).

Good luck

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Subject: NOSE thermostat (NaN & EFG - Error)
From: Maurizio Mattesini <maurizio.mattesini at gmail.com>
Date: 01/26/2015 04:06 PM

I’ve been trying to run a MD calculation (NOSE thermostat) for an Fe-bcc 
2x2x2 supercell (16 atoms)
and always got stuck at the same “EFG - Error”. Please find below the 
input files and the output after
running the min_lapw script. Please note that I’ve been trying to play 
with the nose-frequency value
without getting rid of this EFG/NaN error. Any hints on why I get these 
“NaN” values at the atomic
positions already in the 1st change of the struct file?

-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
WWW:   http://www.imc.tuwien.ac.at/staff/tc_group_e.php
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