Silicon before the bonds break

Abstract

The diamond structure of silicon can be destroyed by a femtosecond-laser pulse in a process that is called nonthermal melting. Using a supercell of 800 atoms, we have performed ab initio molecular dynamics simulations on laser-excited potential energy surfaces for electronic excitation densities around the threshold for nonthermal melting. By introducing a quantitative measure for the resemblance of the atomic paths below and above this threshold, we show that the directions of the atomic motions are the same within 98% during 150–200 fs. The atomic pathways below the melting threshold, before the bonds break, are therefore quantitatively closely related to the atomic motions during the first stages of nonthermal melting.