[Re:01] How to decide ewidth, edelt, and bzqlty

Posted on : April 21, 2017 (Fri) 18:09:05

by Hitoshi GOMI

Hello Ikeda,

Ideally speaking, a larger value is preferable for bzqlty. For edelt, a smaller value is preferable.
But practically speaking, you can use moderate value, depending on your purpose. For example, the equilibrium lattice parameter and the bulk modulus of Cu can be reasonably calculated with bzqlty=3, even though the total energy is not well converged with respect to the bzqlty value.
http://gomisai.blog75.fc2.com/blog-entry-593.html

I usually use edelt=0.001 Ry. Then, I calculate the physical properties (e.g. bulk modulus) with changing the bzqlty, to see the convergence.



For ewidth, neither too large nor too small value is preferable.
As is written in the manual, the range of ewidth must contain all of the valence band. In other words, the bottom of ewidth should locate within a band gap.
http://gomisai.blog75.fc2.com/blog-entry-708.html
http://gomisai.blog75.fc2.com/blog-entry-709.html



In most cases, the absolute value of the total energy is not matter. We only interested in the relative change with changing something (e.g. lattice parameters).
Therefore, the most important point is to keep calculation settings unchanged throughout the series of calculations.

Hitoshi GOMI