Stability of polycrystalline and wurtzite Si nanowires via symmetry-adapted tight-binding objective molecular dynamics

Abstract

The stability of the most promising ground state candidate Si nanowires with less than 10 nm in diameter is comparatively studied with objective molecular dynamics coupled with nonorthogonal tight-binding and classical potential models. The computationally expensive tight-binding treatment becomes tractable due to the substantial simplifications introduced by the presented symmetry-adapted scheme. It indicates that the achiral polycrystalline of fivefold symmetry and the wurtzite wires of threefold symmetry are the most favorable quasi-one-dimensional Si arrangements. Quantitative differences with the classical model description are noted over the whole diameter range. Using a Wulff energy decomposition approach it is revealed that these differences are caused by the inability of the classical potential to accurately describe the interaction of Si atoms on surfaces and strained morphologies.

Kinetically-induced hexagonality in chemically grown silicon nanowires

“…Despite the rareness of WZ Si, Sánchez Dehesa argued that the total energy difference between the two polymorphs (diamond and WZ) of Si is insignificant; instead, the likely reason responsible for the stability of the diamond polymorph is the electrostatic energy [7]. Using the objective molecular dynamics (OMD) approach, Zhang et al calculated energetic stabilizations of WZ Si nanowires (SiNWs) [8]. Nevertheless, it remains unclear whether the same conclusions apply to SiNWs with diameters >10 nm.…”

Electronic structure and optical properties of Si, Ge and diamond in the lonsdaleite phase

“…It is now believed that the tendency of nanowires to crystalize in WZ/LD phase may be true for group-IV semiconductors as well 15 . It has been experimentally found that Si nanowires with a radius in excess of 10 nm tend to crystalize in the LD phase 16 and a number of recent theoretical investigations have confirmed that the hexagonal LD phase is the more stable for Si nanowires exceeding certain critical dimensions [17][18][19][20] . Similar structural phase transitions are expected for Ge nanowires as well 18 .…”

Dislocation onset and nearly axial glide in carbon nanotubes under torsion

“…The popular atomistic modeling tools are unsuitable for modeling this type of deformation. Relying on recent theoretical innovations, 13,14 we describe the CNT's torsional response with objective molecular dynamics ͑MD͒ and predict the possibility of a new mass-conserving nearly axial glide. Such glide cannot be promoted by pure tension.…”

“…The introduced simplifications in the number of atoms allows us to apply an accurate, quantummechanical treatment of the chemical binding. 14 We employ the nonorthogonal two-center tight-binding ͑TB͒ model of carbon 21 as implemented in the computational package TROCADERO. 22 This microscopic model describes well the CNT mechanics.…”