Analysis of long range order

TL;DR

This paper emphasizes the importance of electron-phonon interactions and thermal vibrations in accurately modeling alloy and magnetic phase transitions, challenging traditional models like the Ising model.

Contribution

It introduces a formalism incorporating Debye-Waller Factor corrections into electronic structure calculations for better temperature-dependent modeling.

Findings

Electron-phonon interactions significantly affect ordering energy near transition temperatures.

Inclusion of DWF corrections can reconcile discrepancies between experimental and theoretical ordering energies.

Recent observations support the predicted isotope effects in magnetic phase transitions.

Abstract

A first principles analysis of order-disorder transition in alloys shows that ordering energy is a function of temperature due to thermal vibrations. The inter-nuclear potential energy term converges if zero point vibrations are incorporated and this method can replace the Ewald sum method. Core energy contributions to the ordering energy are stored exclusively in superlattice lines. The effect of electron-phonon interactions on ordering energy is of the same order of magnitude as ordering energy near transition temperatures and cannot be ignored. Ising model and variants are incorrect in explaining alloy phase transitions as they ignore the role of electron-phonon interactions without justification. A theoretical formalism that incorporates the Debye-Waller Factor component of electron-phonon interactions in electronic structure calculations already exists and must be adopted when modeling temperature dependent phenomena. It is suggested that DWF correction will account substantially for the discrepancy between experimental and theoretical ordering energy in Ni3V. Thermal vibrations alter magnetic ordering energy at finite temperatures. The role of electron-phonon interactions in alloy and magnetic phase transitions cannot be ignored and must be incorporated in all models. This will also ensure consistency with x-ray and electron diffraction (alloy transitions) and neutron diffraction (magnetic transitions) results. An isotope effect is predicted for (magnetic) phase transitions if the transition temperature is below Debye temperature. Recent observations of an isotope effect in magnetic phase transitions confirm our above conclusions and imply that the role of electron-phonon interactions must be incorporated in all theories and models of magnetism to avoid contradictions.