[QE-users] SCF Calculation Issue with PBE0 Functional

[Rameswar Bhattacharjee]

Hi Everyone,

I am currently working on an SCF (Self-Consistent Field) calculation
for an organic system using the PBE0 functional. My primary objective
is to obtain a more accurate estimation of the band gap. To achieve
this, I need to determine the energy of the highest occupied level and
the lowest unoccupied level. Due to this requirement, I am unable to
use the smearing method and must set nbnd > nelec/2.

While this approach has been successful for most of the systems I have
tested, I encountered an issue with a few specific systems. For these
systems, the calculation continues to run for an unusually long time,
and I notice that the program prints similar lines (provided below)
after each iteration convergence.

--------------------
    estimated scf accuracy    <       0.00000032 Ry


     convergence has been achieved in   1 iterations


     Using ACE for calculation of exact exchange

     ACE projected onto    50 (nbndproj) and applied to    50 (nbnd) bands
-------------------

I would appreciate it if any of you could offer insights into what
might be causing this problem or suggest potential solutions to
resolve this convergence issue.  Are there any parameters that can be
tuned to achieve the convergence? Your expertise and advice would be
of great help in overcoming this obstacle


-- 
Rameswar Bhattacharjee
Department of Chemistry
Georgetown University
Washington, DC 20057