[CP2K:9842] SIC in qs_ks_utils.F

[Xiaoming Wang]

Hi,

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.

Best,
Xiaoming Wang

On Monday, January 8, 2018 at 11:40:50 AM UTC-5, jgh wrote:
>
> 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 
> <javascript:> 
> Winterthurerstrasse 190 
> CH-8057 Zürich, Switzerland 
> --------------------------------------------------------------- 
>
> -----cp... at googlegroups.com <javascript:> wrote: ----- 
> To: cp2k <cp... at googlegroups.com <javascript:>> 
> From: Xiaoming Wang 
> Sent by: cp... at googlegroups.com <javascript:> 
> 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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