[CP2K:10631] electrostatic decoupling

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

Hi

your problem is related to the ill-defined energy of a charge
in a periodic system.
Your energy 1 is calculated with a background charge to nuetralize
the charge of your orbital. In energy 2, the isolated system,
no such background charge is needed.

If you want to get some idea how to attack this problem, I would
suggest to read the vast literature on the calculation of
charged defects in solids. Start with the recent work of Pasquarello.

regards

Juerg
--------------------------------------------------------------
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: 08/15/2018 10:05PM
Subject: [CP2K:10631] electrostatic decoupling

Hello,

I'd like to decouple the the Coulomb interaction between the electron of one specific state, say HOMO, 
and its periodic images, for a fully periodic DFT calculation. The interested charge density is localized.
I have tried to use different poisson solvers, say MT or WAVELET, to achieve my goal. So first I extracted 
the the charge density from mo_coeff. Then called the poisson solver.

pw_poisson_solve(poisson_env, orb_rho_g%pw, ener1, v_gspace1%pw) 

with poisson environment PERIODIC3D. Next I changed the poisson_env to MT0D, then called  poisson
solver once more.

pw_poisson_solve(poisson_env, orb_rho_g%pw, ener2, v_gspace2%pw)

Finally, the decoupling energy is deltaE = ener1 - ener2. I thought deltaE should be a very small
number, because the charge density of that state is quite localized and my unit cell is big enough for
the MT solver. However, I got a very large deltaE 0.05 Ha. Also the value is negative, which means the 
Hartree energy is higher for the decoupled case. I cannot understand this, because I think the image 
interaction would increase the energy. So can anyone give some advice?

Best,
Xiaoming Wang  
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