[CP2K:9842] SIC in qs_ks_utils.F

[hut... at chem.uzh.ch]

Hi

yes, I think you are right. This SIC method calculates the
electrostatic correction using the same Poisson solver as used
for the full density. For PBC this means that the G=0 term is
neglected and the SIC correction is calculated using a uniform
background charge.

The methods in "calc_v_sic_rspace" use a correction, see
"cp_ddapc_apply_CD" to avoid this problem. A similar correction
would have to be added to the methods in "sic_explicit_orbitals".

The following SIC functionals have a PBC correction
AD
MAURI_SPZ
MAURI_US

No PBC correction is done for
EXPLICIT_ORBITALS (scaled) Perdew-Zunger correction explicitly on a set of orbitals.

best

Juerg Hutter

--------------------------------------------------------------
Juerg Hutter                         Phone : ++41 44 635 4491
Institut für Chemie C                FAX   : ++41 44 635 6838
Universität Zürich                   E-mail: hut... at chem.uzh.ch
Winterthurerstrasse 190
CH-8057 Zürich, Switzerland
---------------------------------------------------------------

-----cp... at googlegroups.com wrote: -----
To: cp2k <cp... at googlegroups.com>
From: Xiaoming Wang 
Sent by: cp... at googlegroups.com
Date: 01/08/2018 06:23AM
Subject: [CP2K:9842] SIC in qs_ks_utils.F

Hello,

In the lines 613 and 614 of the subroutine qs_ks_utils.F, key operations of the SIC correction are shown:
 CALL pw_poisson_solve(poisson_env, orb_rho_g%pw, ener, work_v_gspace%pw)  
energy%hartree = energy%hartree-dft_control%sic_scaling_a*ener 
The first line calculates the electrostatic energy of the unpaired electron (self-interaction) and the second line subtracts this energy from the total Hartree energy. For open boundary calculations, this is correct, since the electrostatic energy calculated this way is the self-interaction energy. However, for periodic boundary conditions, the electrostatic energy calculated by the first line is not the self-interaction energy. Instead, the interaction energy of the unpaired electron and its periodic images is also included!! (Please correct me if I am wrong.)
 So it seems that to do a correct SIC calculation for PBC systems, one needs to either add back the interaction energy of the unpaired electron and its periodic images using perhaps Ewald summation method (not sure) or correct the self-interaction term by changing a poisson solver. Is it possible to calculate the Hartree energy using non-periodic poisson solver, say multipole, for a periodic system?

Best,
Xiaoming


  
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