electrostatic decoupling

[Xiaoming Wang]

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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