Direct Molecular Dynamic Simulation of Light-Induced Structural Change in Amorphous Selenium

Abstract

An amorphous selenium network structure was constructed by combination of a lattice random walk and ab initio molecular dynamic (MD) simulation. The static structure factor, pair correlation function, and vibrational and electronic density of states simultaneously agree with experiment. For the first time, we study structural rearrangement due to light-induced changes in occupation. The predictions of the Kastner et al. valence alternation model are essentially confirmed, and new features of the rearrangement are elucidated. The structural rearrangements are less local than in simple models.

Bonding and elastic properties of amorphous AlYB

“…It was then quenched to 0 K and fully relaxed. This procedure allows for creation of a representative amorphous configuration [28][29][30]. The density was calculated from the energy-volume data.…”

Network structure and dynamics of hydrogenated amorphous silicon

“…The logic is that if the change in occupation (or charge state) causes a significant change in the force, it may be sufficient to cause significant rearrangements in the network, perhaps even the formation of new defects. We have used this approach in a-Se [39], a-As 2 Se 3 [40] and a-Si [29]. This approach is ideal for checking the structural/dynamical consequences of modifying the charge state of a welllocalized dangling bond.…”

Ultrafast defect dynamics: A new approach to all optical broadband switching employing amorphous selenium thin films

“…While this change of occupation is a proxy for what is fundamentally a very complex process, it has the key advantage of offering a reasonable prediction of light-induced structural changes since the electron-phonon coupling is realistic. 30,23 Here, we add an electron from an occupied state to an unoccupied state and let the system evolve freely. We monitored the eigenstates (Kohn-Sham orbitals) of our system around the Fermi-energy and observed the closing of the gap as the lowest unoccupied molecular orbital (LUMO) level descends.…”

“…To theoretically simulate the defect dynamics in the tails and middle of the gap, we began with a 216 atom model of a-Se by Zhang and Drabold 23 and relaxed it to its local minimum using conjugate gradient algorithm 24,25 as implemented by the Vienna Ab-Initio Software Package, VASP. 26,27 The relaxed model is quite realistic and appears to correctly reproduce structural, electronic and vibrational properties of a-Se.…”