Many‐body effects on the electronic and optical properties of Si nanowires from ab initio approaches

Abstract

The study of semiconducting nanowires is one of the most rapidly growing research areas in materials science and nanotechnology, not only from the point of view of the possible applications, but also regarding the use of the latest developments in the theory. In this paper, we review the general ab initio many-body theory and methods and resume some of our very recent results regarding the structural, electronic, and optical properties of Silicon nanowires (Si-NWs), outlining both the reached achievements and some of the technical aspects necessary to obtain them.

Silicon and Germanium Nanostructures for Photovoltaic Applications: Ab-Initio Results

“…A repeated cell approach allows to simulate NCs and NWs. A full geometry optimization is performed and, after the equilibrium geometry is reached, a final calculation is made to obtain not only the occupied but also a very high number of unoccupied Kohn-Sham (KS) eigenvalues and eigenvectors (ε n k , ψ n , k ) [ 24 , 25 ]. In fact, although they cannot be formally identified as the correct quasi-particle (QP) energies and eigenfunctions, they are the starting point to perform MB calculations.…”

“…[ 32 ] for more details). In order to describe correctly the optical response, the solution of the Bethe–Salpeter equation (BSE), where the coupled electron-hole (e-h) excitations are included [ 20 , 25 ], is required. In the Green’s functions formalism, the solution of the BSE corresponds to diagonalize the following excitonic problem …”

Electronic excitations in light absorbers for photoelectrochemical energy conversion: first principles calculations based on many body perturbation theory

“…Many theoretical studies appeared in the literature on the optical properties of SiNW. [244][245][246][247][248][249][250] Two fundamental effects were taken into account in order to obtain physically sound results: 251 (i) local field effects, which lead to a strong suppression of the absorption of light polarized perpendicular to the NW axis, dramatically increasing the optical anisotropy of the system; (ii) excitonic effects, which are stronger in one dimensional systems, due to the spatial overlap between electron and hole wavefunctions. Due to excitonic effects, the absorption spectra of wires can be red shifted and their oscillator strength can be redistributed, with respect to those of the bulk.…”

Thermal stabilization of thin gold nanowires by surfactant-coating: a molecular dynamics study

“…For the purpose of nanoscale applications, a quantitative understanding of the structural and thermodynamic properties of such NWs is a prerequisite. Manipulating these tiny physical systems poses a challenge to many existing experimental techniques [10] and to complement experiments, a variety of computational studies have focused on thermal, mechanical, and electrical properties of metal nanosystems using mostly classical molecular dynamics (MD) simulation [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] and quantum chemical ab initio calculations [28][29][30][31].…”

“…Manipulating these tiny physical systems poses a challenge to many existing experimental techniques 10 and to complement experiments, a variety of computational studies have focused on thermal, mechanical, and electrical properties of metal nanosystems using mostly classical molecular dynamics (MD) simulation [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] and quantum chemical ab initio calculations. [28][29][30][31] One substantial difference between metal NWs and their bulk phase is the fact that the melting of NWs occurs at substantially lower temperatures than in the corresponding bulk material. This 'melting point depression' has been known for a long time from metal nanoparticles (NPs).…”