Incomplete melting of the Si(100) surface from molecular-dynamics simulations using the Effective-Medium Tight-Binding model

In this thesis a new model for calculating the total energy of atomic and solid systems is presented. The model is used to study the properties of the Si(100) surface and dislocation dynamics in the diamond structure. For the Si(100) surface the main result is the finding of an incomplete melted state at $1550^0 K$. The studied dislocation is the $90^0$ partial and it is found that the barriers for kink formation and migration are in good accordance with experimental observat...

Recent low-temperature scanning tunneling experiments have challenged the generally accepted picture of buckled silicon dimers as the ground state reconstruction of the Si(100) surface. Together with the symmetric dimer model of the surface suggested by quantum chemistry calculations on small clusters, these findings question our general understanding of electronic correlations at surfaces and its proper description within density functional theory. We present quantum Monte C...

The structural features of the interface between the cystalline and amorphous phases of Si solid are studied in simulations based on a combination of empirical interatomic potentials and a nonorthogonal tight-binding model. The tight-binding Hamiltonian was created and tested for the types of structures and distortions anticipated to occur at this interface. The simulations indicate the presence of a number of interesting features near the interface. The features that may lea...

Motivated by the controversy between quantum chemists and solid-state physicists, and by recent experimental results, spin-polarized density-functional (DFT) calculations are used to probe electron correlation in the Si(100) reconstructed surface. The ground state displays antiferromagnetic spin polarization for low dimer inclinations indicating, not magnetic order, but the importance of Mott-like correlations among dangling bonds. The lowest energy corresponds to a higher di...

We simulate the liquid silicon surface with first-principles molecular dynamics in a slab geometry. We find that the atom-density profile presents a pronounced layering, similar to those observed in low-temperature liquid metals like Ga and Hg. The depth-dependent pair correlation function shows that the effect originates from directional bonding of Si atoms at the surface, and propagates into the bulk. The layering has no major effects in the electronic and dynamical propert...

It is experimentally observed and theoretically proved that the distance between topmost layers of a metal surface has a contraction. However, well-known potentials such as Lennard-Jones and Morse potentials lead to an expansion of the surface inter-layer distance. Such simple potentials therefore cannot be used to study metal surface relaxation. In this paper, extensive Monte Carlo simulations are used to study the silver (111) surface with both the Gupta potential (GP) and ...

A new method for calculating the total energy of Si systems is presented. The method is based on the effective-medium theory concept of a reference system. Instead of calculating the energy of an atom in the system of interest a reference system is introduced where the local surroundings are similar. The energy of the reference system can be calculated selfconsistently once and for all while the energy difference to the reference system can be obtained approximately. We propo...

The molecular dynamics (MD) approach is an effective tool for investigating atomistic dynamical phenomena at the surface of materials under strong laser irradiation. Therefore, numerous laser ablation MD simulation studies have been conducted to date. However, in most MD studies, non-thermal and entropic effects via hot electrons on interatomic interactions that could cause significant differences in the simulation results are not considered. In this study, the MD simulation ...

Modern semiconductor applications demand precise laser processing at the nanometer scale, requiring a detailed understanding of phase transitions and structural modifications. Accurate control over laser-induced processes in semiconductors is essential for generating surface structures and modifying surface properties. In this study, we present a numerical investigation of non-equilibrium laser-induced phase transitions in silicon (Si) using a hybrid atomistic-continuum model...

A reliable description of surfaces structures in a reactive environment is crucial to understand materials functions. We present a first-principles theory of replica-exchange grand-canonical-ensemble molecular dynamics (REGC-MD) and apply it to evaluate phase equilibria of surfaces in reactive gas-phase environment. We identify the different surface phases and locate phase boundaries including triple and critical points. The approach is demonstrated by addressing open questio...