arXiv subjects

Simone Selenu

Publications and source records attributed to Simone Selenu.

5 recordsLinked to original sources

arXiv2010

Variations of polarisation in cerystals

It is nowadays a quite diffuse idea that variations of electronic polarisation, as introduced by Resta[1], in condensed matter theory are related to a "Berry phase"[2], as shown by Vanderbilt. The derivation of the latter geometric phase is correct and the periodic gauge[2] is used for its derivation, aside not allowing for its calculations in finite electromagnetic fields. Its derivation has not been demonstrated in the general case of an external homogeneous electric field interacting with the electronic field. In the present paper we give a brief derivation of the algorithm for the calculations of polarisation differences in a general manner than in[2] defining it even in the presence of an external electric field interacting with the electronic field and writing equations in a way directly implementable in modern first principles codes[1,2]

cond-mat.other↗

arXiv2009

Variations of polarisation in external electrostatic fields

It is nowadays a quite diffuse idea that variations of polarisation in condensed matter theory are related to a "Berry phase". The derivation of the latter geometric phase is correct $\it{only if}$ the restrictive periodic gauge\cite{KS-V} is used for its derivation, aside giving rise to a "quantum of polarisation" that is of difficult theoretical interpretation. Its derivation has not been demonstrated in the general case of an external homogeneous electric field interacting with the electronic field. In the present paper we give a brief derivation of the polarisation differences in a general manner than in\cite{KS-V} allowing for a general boundary conditions freedom showing that is possible to define it even in the presence of an external electric field interacting with the electronic field and writing equations in a way directly implementable in modern first principles codes.

cond-mat.mtrl-sci↗

arXiv2008

Geometric phase in external electromagnetic fields

Variations of polarization of the electronic field is a dielectric property quantified by Resta et al. and discovered to be a Berry phase of the electronic subsystem. In order to continue the previous research we wrote a scalar phase Φas the circulation of the polarization field or in alternative and in a more general form as the flux of a new vector field called macroscopic rotonic field. The latter shows to be a more general scalar Berry phase concerning the interaction of the electronic subsystem with an external electromagnetic field.

cond-mat.mtrl-sci↗

arXiv2006

Power and group velocity

Here we make use of the Hellmann-Feynman theorem, with the aim to calculate macroscopic quantum velocities instead of forces, and we show how it is possible to derive the expression of the work per unit time, per unit volume (power density) done by a static external uniform electromagnetic field interacting with a quantal body.

cond-mat.mtrl-sci↗

arXiv2006

Conserved geometric phase and group velocity

In this paper we make use of the concept of conserved geometric phase and of group velocity,in conjunction with the representation theory\cite{Dirac,Dirac-letture}, in order to derive some relevant physical quantities for the description of the dielectric and magnetic response of crystalline materials. As an application of the model, we derive the expression of the macroscopic dipole moment per unit volume, and the expression of the current induced by a uniform static external electromagnetic field.

cond-mat.mtrl-sci↗