[CP2K:9847] SIC in qs_ks_utils.F

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

Hi

I am not familiar with the details of the different SIC codes.
I currently don't have the time to look deeper into this.

regards

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
---------------------------------------------------------------

-----"Xiaominng Wang" <wxia... at gmail.com> wrote: -----
To: <hut... at chem.uzh.ch>
From: "Xiaominng Wang" <wxia... at gmail.com>
Date: 01/10/2018 09:43PM
Subject: RE: [CP2K:9847] SIC in qs_ks_utils.F

Dear Prof. Hutter,

Thanks.  But how to activate the ddapc correction? I checked both EXPLICIT_ORBITALS and MAURI_SPZ 
methods for a charged (+1) box with PBC, the results of the two are exactly the same.

Btw, I think I need to go for Scaled PZ with explicit orbitals anyway, since the SIC methods with PBC correction (AD, MAURI) are only 
suitable to either isolated systems or doublet cases and my system is in singlet  or triplet configurations with full PBC.
I am planning to do some modifications of the code to include this correction. Do I need to make any further changes of 
following lines if I want to add them to sic_explicit_orbitals?
---------------------------------------------------

      CALL cp_ddapc_apply_CD(qs_env, &
                             orb_rho_g, &
                             ener, &
                             v_hartree_gspace=work_v_gspace, &
                             calculate_forces=calculate_forces, &
                             Itype_of_density="SPIN")
-----------------------------------------------------

Best,
Xiaoming Wang


-----Original Message-----
From: cp... at googlegroups.com [mailto:cp... at googlegroups.com] On Behalf Of hut... at chem.uzh.ch
Sent: Monday, January 8, 2018 11:41 AM
To: cp... at googlegroups.com
Subject: Re: [CP2K:9847] SIC in qs_ks_utils.F

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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