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[Latévi Max LAWSON DAKU <max.lawson@unige.ch>]

Dear Abinit users,

I would like to study a family of related metallic systems.
For the one with the simplest molecular formula (6 atoms
in the formula unit), I tried to do a convergence study in
order to determine the optimal value of tsmear (cold
smearing; occopt=5).

1) Without smearing, I did full geometry optimisation with
   nkpt = 10, 28, 60 and ecut values of 20, 30, 40, 50 Ha
   (and an additional test optimisation with nkpt=60 and
   ecut=80). For this FCC system, this gives "converged"
   values of acell=7.260 angstrom and Etot=-167.260 Ha.
   The "(tsmear=0)-convergence" in acell (> 0.001 A) is
   obtained for ecut=40  Ha and nkpt=28.


2) With ecut set to 40 Ha and smearing turned on, I made
   vary tsmear at fixed values of nkpt (10 pts -> circles;
   28 pts -> squares; 60 pts -> diamonds). The attached
   figures gives the dependences of acell and Etot on
   tsmear. For tsmear <= 0.01 Ha, acell=2.589 A and
   Etot=-167.266 Ha; independantly of the integration
   grid used. The curves are actually similar in the studied
   range.

3) Given these results, I would go with a tsmear value of
   4 mHa and nkpt=10 for the determination of the bulk
   modulus and its derivative, and  also of the phonons.

Comments, criticism are welcomed.

Thanks in advance,
Max




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Latevi Max LAWSON DAKU
Departement de chimie physique 
Universite de Geneve - Sciences II
30, quai Ernest-Ansermet  
CH-1211 Geneve 4 
Switzerland 

Tel: (41) 22/379 6548 ++ Fax: (41) 22/379 6103
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