Computation of flexoelectric coefficients of a MoS2 monolayer with a model of self-consistently distributed effective charges and dipoles
Résumé
Flexoelectricity is an electromechanical coupling phenomenon that
can generate noticeable electric polarization in dielectric
materials for nanoscale strain gradients. It is gaining increasing
attention because of its potential applications and the fact that
experimental results were initially an order of magnitude higher
than initial theoretical predictions. This stimulated intense
experimental and theoretical research to investigate flexoelectric
coefficients in dielectric materials such as two-dimensional
materials. In this study, we concentrate on the calculation of the
flexoelectric coefficients of 2D-MoS2 due to a model using
self-consistently determined charges and dipoles on the atoms. More
specifically, we study the importance of two contributions that
were neglected/omitted in previous papers using this model, namely,
the charge term in the total polarization and the conservation of
electric charge through a Lagrange multiplier. Our calculations
demonstrate that the results for flexoelectric coefficients
computed with this improved definition of polarization agree better
with experimental measurements, provided that consistent
definitions for signs are used. Additionally, we show how two
physical contributions with opposite signs compete to give net
values of flexoelectric coefficients that can be either positive or
negative depending on their relative importance and give net values
for the case of MoS2.
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