How to decide ewidth, edelt, and bzqlty

Posted on : April 21, 2017 (Fri) 01:20:57

by 池田敦俊

Dear AkaiKKR users,

I am very sorry for asking many questions.
Since I'm not a specialist of the calculations of electronic states, every calculation gives me another question.

In this great blog (http://gomisai.blog75.fc2.com/blog-entry-591.html), the total energy of copper as a function of bzqlty is shown, and we see that the energy remains somewhat unchanged with bzqlty >= 8.
I tried similar check on ewidth, edelt, and also bzqlty.
However, no such convergence of energy is obtained in my case.
I'm wondering if there is an objective way to decide the proper values for these parameters.
Maybe I am too nervous of the parameters.

Here I will explain what I did and what I got.
Detailed input file is attached in the end of this post.

First, I calculated with edelt=0.001, ewidth=4.0, and bzqlty=4.
Then I found that the bottoms of the energy bands are located at 2.7, 1.9, 1.5, 0.7, and 0.4 Ry below the Fermi energy.
(I don't know about the bands below -3 Ry, which are out of range of the DOS calculation.)

I fixed edelt=0.001 and bzqlty=4, and decreased ewidth.
The obtained total energies are as follows:
-------------------
ewidth energy
2.7 -31582.4764466
1.9 -31582.5312236
1.5 -31582.5662046
0.7 -31582.5865802
0.4 -31571.8323648
-------------------
If we neglect ewidth=0.4 Ry, the energy gets larger and larger if I increase ewidth.
I don't know where to stop.
To my eyes, the band just above -2.7 Ry looks fairly narrow, or the density of state is sharp, suggesting that this band is a core state.
Therefore I chose to set ewidth=1.9, but I'm not sure this is the best value or not.

Next, I fixed edelt=0.001 and ewidth=1.9, and increased bzqlty.
The obtained total energies are as follows:
------------------
bzqlty energy
4 -31582.5312017
5 -31582.5322586
6 -31582.5312146
7 -31582.5324347
8 -31582.5325331
9 -31582.5325039
10 -31582.5333232
11 -31582.5332628
------------------
Without bzqlty=10 and 11, I would think that bzqlty=8 is enough, but the energy suddenly drops at bzqlty=10.
I chose bzqlty=10, but I'm afraid that the energy may drop again at bzqlty=12, possibly 20 or even larger.

Finally, I fixed ewidth=1.9 and bzqlty=10, and changed edelt from 0.01 to 0.0001.
The obtained total energies are as follows:
----------------------
edelt energy
0.01 -31582.5609261
0.005 -31582.5517688
0.002 -31582.5355211
0.001 -31582.5308982
0.0005 -31582.5409966
0.0002 -31582.5634297
0.0001 -31582.5809119
----------------------
The energy has a maximum at edelt=0.001.
I have no idea why this maximum appears nor which edelt is the best.
Is the smaller the better?

I would really appreciate it if someone could answer this very long question.

Sincerely,
Ikeda


Below is an example of my calculation.
I changed edelt, ewidth, and bzqlty of this input.
c----------------------Sr3SnO--------------------------------
go data/Sr3SnO_ewidthScan
c------------------------------------------------------------
c brvtyp a c/a b/a alpha beta gamma
sc 9.71206 , , , , , ,
c------------------------------------------------------------
c edelt ewidth reltyp sdftyp magtyp record
0.001 2.7 srals pbe nmag 2nd
c------------------------------------------------------------
c outtyp bzqlty maxitr pmix
update 4 100 0.03
c------------------------------------------------------------
c ntyp
3
c------------------------------------------------------------
c type ncmp rmt field mxl anclr conc
Sr 1 1 0.0 2 38 100
Sn 1 1 0.0 2 50 100
O 1 1 0.0 2 8 100
c------------------------------------------------------------
c natm
5
c------------------------------------------------------------
c atmicx atmtyp
0 0 0 Sn
0 0.5 0.5 Sr
0.5 0 0.5 Sr
0.5 0.5 0 Sr
0.5 0.5 0.5 O
c------------------------------------------------------------