# Dielectric polarization: how to identify what part of the total polarization (dipolar+electronic+ionic) I need (conceptual question, I use DFPT, VASP)

I am doing polarization calculations to get data for use in other calculations. To start with, I want to calculate the static dielectric constant. However, I'm a newbie to polarization and it is a struggle to relate my calculation output to the static dielectric constant. If someone could point me in the right direction, I would be grateful. I'm using VASP software for the first time.

The total polarization is mainly the sum of dipolar, ionic, and electronic terms. VASP implements a method (DFPT; density functional perturbation theory) for polarization calculations that seems to calculate only the ionic and electronic terms. This is a concern because my fluid may have a significant dipolar component. If anyone thinks I'm wrong on this, a heads-up would be great.

The reason I mentioned that DFPT may only calculate the ionic and electronic contributions to total polarization is that I have managed to get VASP output for the electronic term. In the output file (.xml, for any VASP aficionados), it is in the form of a dielectric function that has six elements. Three of the elements belong to a "real" part and three belong to an "electronic" part of the dielectric function. From my reading, it looks like the "real" part should somehow correspond to the static dielectric constant. My question is, which part of the total polarization is this likely to represent?

In other words, does each of the three terms in the total polarization contribute to the static dielectric constant, where this one is likely to be the electronic contribution? Or is the output I have likely to be the total (dipolar too) static dielectric constant? I ask because I read that only the dipolar and ionic terms contribute significantly to the static dielectric constant.

• I'd ask this question over in mattermodeling.stackexchange.com - there are more VASP users over there. – Geoff Hutchison Mar 25 at 3:42
• @GeoffHutchison, thank you. Yes, there are even VASP and DFPT tags there. I tried but one of the moderators deleted the bottom two paragraphs and it didn't make sense or address what I needed, so I thanked him, deleted it, and moved it here. – NTS Mar 25 at 6:48