Hello All! I'm trying to calculate a system with a *known* AFM ground state. In the attached example, I provide the input data I'm using for CuMnAs -- a tetragonal anti-ferromagnet. I've started on this project by first executing the examples, and particularly FeO. I tested this example against all sorts of variations: different functionals, with/without U, and so on. Without any further tweaking, the system always converged to the AFM ground-state, provided the initial moments were also oriented in the AFM configuration.
Which makes my failure in this (CuMnAs) system even more puzzling. Firstly, *without* any constraints, the system does not converge to an AFM state. 1. Using 'constrained_magnetization=total' leads to completely wrong results, with a divergent "Magnetic field". 2. A more-or-less sensible result can be obtained with 'constrained_magnetization='atomic' (as shown), however, the resultant magnetization is not altogether anti-ferromagnetic. Note that the system is in general endowed with PT-symmetry. The resultant eigenvalues *DO NOT* show this and you can also see the disparity in the magnetic moments of the Mn atoms, as well as eigenvalue difference of more than 1meV for some bands and k-points. 3. This behavior is *weakly* dependent on lambda. I tried fiddling around with the values. A certain increase worsens the results, then seems to improve it, only to worsen again. What is a reason value for the constraint, in your estimation? I take it to be 5% of the unperturbed energy (i.e., energy without the constraint). 4. Testing the *exact* same system on different software (VASP, in this case), converged very well to the AFM state (i.e., PT symmetry was recovered to less than 1meV). What am I doing wrong, therefore? I would appreciate any advice. Yours thankful, Daniel Kaplan Dept. of Condensed Matter Physics Weizmann Institute of Science
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