[Wien] Convergence problem for the slab calculation!

[L. D. Marks]

Several things:

1) What is the "Warning" that you are getting? You need to look at the scf 
code to see what this is due to. Please check the archives (and/or the 
user guide) about what you find.

2) Inspecting the energy (:ENE) and charge (:DIS) are relics of "the bad 
old days", as is reducing the mixing coefficient to values like 0.01. The 
correct way to look at these problems is to look at the behavior of the 
plane waves (:PLANE) and the angle between the Broyden and Pratt steps 
(:DIRB); run the script attached. If this angle is large (say > 50 
degrees) you need to reduce the plane wave scaling in the mixer. You 
should also look at the total plane wave interstitial charge (grep -e "CTO 
"), sometimes this just takes time to converge particularly for a surface.

3) There are a few cases (rare) when reducing the plane wave scaling does 
not work (by itself) and one has to also reduce the mixing coefficient to, 
say, 0.05 or even less. I suspect that most of these are cases where the 
physics is not properly defined in the calculation, e.g. one should be 
using more k-points or running spin polarized.

On Tue, 20 Dec 2005, 蔡 孟秋 wrote:

> Dear wien2k user
>
> As a test, I am calculating the BaTiO3 surface with nine layers slab and the 
> same thickness vacuum. I used a Rkmax of 7 and gmax of  14 with the mixing 
> coefficient of 0.1 and even 0.01. Moreover, I correct the E-parameters in 
> case.in1 to replace all "0.3" by appropriate values 0.1 (below our EF about 
> 0.25). But I get energy oscillations in the scf cycle.
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177777.148950
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177776.243123
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177776.971894
> :ENE  : *WARNING** TOTAL ENERGY IN Ry =      -177775.571717
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177775.294152
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177775.176350
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177775.170225
> :ENE  : *WARNING** TOTAL ENERGY IN Ry =      -177775.117307
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177775.182107
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177775.115802
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177775.106464
> :ENE  : *WARNING** TOTAL ENERGY IN Ry =      -177775.124568
> :ENE  : *WARNING** TOTAL ENERGY IN Ry =      -177775.107141
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177775.191016
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177775.104630
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177775.107498
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177775.241324
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177775.097320
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177775.095030
> :ENE  : ********** TOTAL ENERGY IN Ry =      -177775.119517
>
>
> Could exist any other problem?
>
> Thank you!! for your time and advise.
>
> Dr. Cai
>
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Note: if you have an old email address for me, please note that "nwu" has
been changed to "northwestern".
-----------------------------------------------
Laurence Marks
Department of Materials Science and Engineering
MSE Rm 2036 Cook Hall
2220 N Campus Drive
Northwestern University
Evanston, IL 60201, USA
Tel: (847) 491-3996 Fax: (847) 491-7820
email: L-marks at northwestern dot edu
http://www.numis.northwestern.edu
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