[Wien] Questions about running WIEN2k with amorphous materials

[YOOSOO YI]

Dear all,



I’m running WIEN2k 14.2 on CentOS 6.6, and it looks like there are no
problems when I’m trying to calculate crystalline materials till now. I
have some questions about how to use the WIEN2k package for the amorphous
systems. Since I have used this program almost 5 years, I know that this
program is designed for the crystalline materials. Recently, I have tried
to calculate the electronic properties for amorphous silicate oxides with
taking a P1 symmetry to a unit cell, and of course the amorphous atomic
configurations are obtained from the other program based on the PAW-type
pseudopotential method.



Followings are the questions that I have.



The first question is about the possibility of calculating the electronic
properties for amorphous materials using WIEN2k program. If I had obtained
the amorphous atomic configurations of silicate oxides using the other
program, is it possible to calculate the electronic structures of amorphous
silicate oxides using WIEN2k? I think that it might be possible if I make a
sufficiently large super cell which is containing enough number of atoms
that can ignore the boundary effect due to the periodic boundary condition.
Is it right?



The second question is about using SGROUP program for the amorphous
materials. The case.struct file generated from the case.cif file of
amorphous materials, using CIF2STRUCT script, has same atomic coordinates
with the case.cif file. However, the case.struct_sgroup file generated from
SGROUP program has completely different atomic coordinates, relatively. All
the atoms in the case.struct_sgroup file are re-positioned and some of
atoms are moved to edges/vertexes of a unit cell, and it might for taking a
higher symmetry. I know that I should not use this case.struct_sgroup file
when I tried to calculate the electronic structures of crystalline
materials including core-hole on atoms in a unit cell, i.e., should take P1
symmetry as supercell. But, for amorphous system, each generated
case.struct and case.struct_sgroup file has same P1 symmetry even though
they have different relative atomic coordinates. In this case, can I use
this case.struct_sgroup generated from SGROUP? If not, what is the reason?



The third question is about calculating the electronic properties for
amorphous materials using WIEN2k. Recently, I have been trying to calculate
a partial DOS for amorphous silicate oxides. However, the unexpected ERROR
is continuously occurred on the LAPW1 in the first step of SCF calculation
with a simple error message in the lapw1.error file: “Error in LAPW1”. I
had tried to figure out the reason of this error from the WIEN2k FAQ and
User Guide, and after researching, I had found that this problem, i.e.,
stopping of calculation on the LAPW1 in the first step of SCF calculation,
could be induced from an unacceptable potential function generated from
LAPW0 unless there are problems on other parameters, e.g., RKMAX, GMAX,
E-values, etc. It means that the case.struct_sgroup file could be the
origin of this problem, since there were no problems when I was trying to
calculate the electronic structures for the crystalline material which is
the starting configuration used in the FPMD simulation. Therefore, in this
case, I had thought that this unexpected ERROR on the LAPW1 might be caused
from using the case.struct_sgroup file generated by SGROUP. Now, my
question is that is this procedure for solving this problem right? If not,
please give me other advises.



This is the fourth question. After researching some references, I have
tried to calculate a partial DOS for amorphous silicate oxides without
using case.struct_sgroup file, and the problem was looked like solved.
However, after the first step of SCF calculation is finished, another ERROR
is occurred on LAPW2 with an error message related to the ghost band. To
solve this problem, I had tried to modify the case.inm file to change the
mixing scheme from MSR1 to MSEC1, but it did not help. Then I thought that
I had to modify the energy parameters in case.in1c file, especially
“EF=###” and “GLOBAL AE-PARAMETER with n OTHER CHOICES”. Note that, after
the first step of SCF calculations, the “EF=###” value in case.in1c file
changes from its default value (EF=0.5 Ry) to EF=0.1 Ry. However, now, I am
trying to change “EF=###” value to ~0.6 Ry that is obtained from the SCF
calculation for the crystalline structure used in the FPMD simulation as
the starting configuration. Now, these are the questions. Should I
retain/use this “EF=0.1” value to restart the SCF calculation, or should I
have to change this to another value, e.g., “EF=0.5 Ry”. Or, should I
change all the energy parameters in case.in1c file “0.30” to another value?
Do you have any other suggestions for this problem? And furthermore, what
is the meaning of GLOBAL E-PARAMETER and ENERGY PARAMETER for each
L-resolved state in the case.in1c file? Does ENERGY PARAMETER for each
L-resolved state indicate the exceptions of choosing basis sets from
globally defined GLOBAL E-PARAMETER in its above line?



This is the last question, about the case.in1c file used for LAPW1. I want
to understand the differences among these following cases.



Set-A) Using -6.0 Ry as a core-valence separation energy

Set-B) Using -11.0 Ry as a core-valence separation energy

Set-C) Using -6.0 Ry as a core-valence separation energy & Modifying
case.in1c file same as in case.in1c file in Set-B



Set-B has the largest number of valence electrons in case.in2c file, and
the smallest total occupation number in case.inc file. And the case.in2c
and case.inc file in both Set-A and Set-C have same number of valence
electrons and occupation number, but they have different case.in1c file. Do
the additional lines in case.in1c file of Set-C indicate more flexible
representations of electronic orbitals than in the Set-A? What is the
meaning of additional local orbitals in case.in1c file?



Thanks for reading such long questions. Any help will be gratefully
appreciated.


Best regards, YOOSOO
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