﻿

Fixing the spin at each atom

Total energy, DFT+U, BigDFT,...

Moderator: amadon

senersen
Posts: 1
Joined: Thu Apr 30, 2015 9:34 am

Fixing the spin at each atom

Dear users

I have a problem which can be (i think) solved by fixing the spin value at each atom. The problem is as follows;

I am trying to calculate the ground state of an anti-ferromagnetic (AFM) system. Although i know the value of final spins approximately, i do not know the lattice constant and position of the atoms for that system. When i start from the spin unpolarized geometry or from AFM geometry obtained with some other pseudopotential i get 0 magnetic moment at each atom. Therefore, i thought, to be sure that i cannot have AFM state with this pseudopotential, i need to fix the spin of each atom to the value that i expect and relax the system for the geometry. Then, after obtaining the optimized geometry i can relax the geometry and spin values together to see if it is going to go zero again or give me some spin value.

I could not find a variable that tells abinit to keep the spin at each atom fixed. Does anyone know how to do it or how to solve my problem woth some other method?

Cheers,

sener

ebousquet
Posts: 370
Joined: Tue Apr 19, 2011 11:13 am
Location: University of Liege, Belgium

Re: Fixing the spin at each atom

Dear Sener,
You have the magconon and magcon_lambda input variables to fix the spin value on each atom:
http://www.abinit.org/doc/helpfiles/for-v8.0/input_variables/html_automatically_generated/vargs.html#magconon
It should constrain the magnetisation in a sphere around each atom to the one you specify in the spinat input flag.
You'll have to play a bit with the constraint factor lambda to find the right regime.
Best wishes,
Eric