My Community

Dear all,
I am trying to get some feedback with defects in bulk. Honestly I do not know if I am moving towards the right direction. I read the manual (Dipole corrections for defects in solids) but I still have trouble.
Here are my doubts.

I have a 64 atom cell of GaAs and I want to replace one Ga with 1 Si, studying it first as a neutral, then as charged -1.

As neutral case,
1) I optimize my neutral cell (with Si replacing Ga) and I get my energy (in principle there should be not so large effects due to dipole corrections since neutral system).

As a charged defect
2) I want to study the system charged -1. Then I input a new NELECT (= initial + 1e-). Then I optimize. (the manual states to calculate first energies WITHOUT corrections)

3) To correct the dipole/quadrupole, and energy, I restart setting DIPOL= (coor of the def) and LDIPOL=.TRUE.


Since I get two TOTEN values, one from 2) and one from 3), my question is:

Must the value I get for the corrections (dip/quad/Energy) be added by hands (as I read in the manual) on the energy calculated in 2)

Or the TOTEN I have to take into account is DIRECTLY that calculated 3)

I am honestly in trouble.... The more I read messages in the forum and the manual the less I am able to give me an answer.

Please help me,
thanks!
G

for the higher multipole corrections, please keep in mind that
-- you have to check first (by having a look at the charge density difference of the perfect and the defect cell) whether the charge is localized (in the defect)
-- as written in the manual, just set IDIPOL=4; DIPOL (coordinates), and LDIPOL=.False. because the automatic correction is not possible in vasp.4.6,
-- then calculate the defect induced quadrupoles by taking the difference of Tr[quadrupole] of the perturbed and the unperturbed cell. rescale the contributions to the multipole corrections according to the manual
(dipole-quadrupole, monopole-quadrupole), add the monopole-monopole contributions and finally re-scale with the multipole corrections with dielectric constant ε. It can be found in standard reference handbooks for many solids. vasp.4.6 does not offer the calculation of ε from ab initio.
concerning TOTEN as written in OUTCAR: the very last TOTEN written for each ionic step (i.e.after electronic convergence is achieved) includes the dipol energy. You can easily check this contribution by "grep TOTEN OUTCAR"

Bear in mind that once you change NELECT (or put a defect in your system), your eigenvalues are shifted, which requires further corrections. I prefer to figure out the potential alignment and image charge corrections by hand, and forget about built in tags like IDIPOL et al.

Thanks a lot. But could you kindly be more explicit? Can you explain me how to do it? Are there any restrictions for this procedure?
I am treating 1 Ge substitituting Ga and As at once, respectively, and on this system I am varying the charge (NELECT) from -2 to +2. How to correct by hands charge effect? Must the defect still localized? My very best and thanks in advance,
G

An explicit and exhaustive explanation is beyond the scope of this forum
See e.g. PRB 78, 235104 (2008).