Computation of flexoelectric coefficients of a MoS2 monolayer with a model of self-consistently distributed effective charges and dipoles

Abstract

International audienceFlexoelectricity is an electromechanical coupling phenomenon thatcan generate noticeable electric polarization in dielectricmaterials for nanoscale strain gradients. It is gaining increasingattention because of its potential applications and the fact thatexperimental results were initially an order of magnitude higherthan initial theoretical predictions. This stimulated intenseexperimental and theoretical research to investigate flexoelectriccoefficients in dielectric materials such as two-dimensionalmaterials. In this study, we concentrate on the calculation of theflexoelectric coefficients of 2D-MoS2 due to a model usingself-consistently determined charges and dipoles on the atoms. Morespecifically, we study the importance of two contributions thatwere neglected/omitted in previous papers using this model, namely,the charge term in the total polarization and the conservation ofelectric charge through a Lagrange multiplier. Our calculationsdemonstrate that the results for flexoelectric coefficientscomputed with this improved definition of polarization agree betterwith experimental measurements, provided that consistentdefinitions for signs are used. Additionally, we show how twophysical contributions with opposite signs compete to give netvalues of flexoelectric coefficients that can be either positive ornegative depending on their relative importance and give net valuesfor the case of MoS2