[Wien] Convergence problem

[tran at theochem.tuwien.ac.at]

The calculation for an isolated atom with a code which uses periodic
boundary conditions (like WIEN2k) is not trivial. This is what I have done
recently for most atoms of the periodic table (excluding f-systems), and
for some of the transition-metal atoms this was extremely difficult to
achieve convergence.

A few hints (that I used):

1) It is important (and necessary depending on the atom) to reduce the
symmetry from cubic to, e.g., orthorhombic to be able to access the
electronic configuration with the lowest energy (this is the procedure
followed by several research groups like VASP for instance).
If necessary I can give more details about the case.struct that I used.

2) lapw0 requires a lot of memory, while lapw1 requires both
memory and time. To reduce computer time for lapw1, I was using
iterative digonalization (this was my command for all atoms):
runsp_lapw -ec 0.0001 -cc 0.0001 -it -i 1000 -NI

3) For the Ni atom the magnetic moment should be 2:
:MMTOT:  SPIN MAGNETIC MOMENT IN CELL     =    2.00238

4) I was using the default setting for mixer.

F. Tran

On Sun, 28 Dec 2014, Laurence Marks wrote:

> 
> Also, only 1 k-point (Gamma), an RMT and RKMax similar to what you use for
> bulk Ni, particularly as I assume you are doing the calculation to get an
> enthalpy of formation. You may have to use the mpi versions as it is
> probably too large for a non-mpi run.
> 
> If you are doing WC+U (or -ineece) the U (or on-site hybrid) removes the
> phase transition so convergence should be simple.
> 
> Straight WC is not a simple calculation because the physics for an isolated
> Ni atom is wrong. With wrong physics there is in fact no guarantee that the
> calculation will ever converge!
> 
> ___________________________
> Professor Laurence Marks
> Department of Materials Science and Engineering
> Northwestern University
> www.numis.northwestern.edu
> MURI4D.numis.northwestern.edu
> Co-Editor, Acta Cryst A
> "Research is to see what everybody else has seen, and to think what nobody
> else has thought"
> Albert Szent-Gyorgi
> 
> On Dec 28, 2014 11:47 AM, "Laurence Marks" <L-marks at northwestern.edu> wrote:
>
>       You almost certainly need to run spin polarized, probably MSR1
>       (GREED 0.1), TEMPS (room temp). The convergence is complicated
>       for WC (& simple GGAs) due to an electronic phase transition
>       between sp & d occupation near the fixed point.
>
>       ___________________________
>       Professor Laurence Marks
>       Department of Materials Science and Engineering
>       Northwestern University
>       www.numis.northwestern.edu
>       MURI4D.numis.northwestern.edu
>       Co-Editor, Acta Cryst A
>       "Research is to see what everybody else has seen, and to think
>       what nobody else has thought"
>       Albert Szent-Gyorgi
>
>       On Dec 28, 2014 10:47 AM, "Muhammad Sajjad" <sajjadpu at gmail.com>
>       wrote:
>             Dear Users I am running SCF calculation for Ni with
>             lattice constant of 30 Bohr and using WC-GGA. The
>             calculation is not converging even upto 100
>             iterations and more. To solve the problem I have
>             performed following steps
> 
> switched to TEMPS = 0.005 from TETRA
> Changed MSR1 to PRATT
> changed mixing factor (increase and decrease from 0.2)
> 
> Thanking in advance. 
> 
> Dr. Sajjad
> 
> 
>