Stable isomers and electronic, vibrational, and optical properties of WS2 nano-clusters: A first-principles study

Abstract

In this paper, we employ an evolutionary algorithm along with the full-potential density functional theory (DFT) computations to perform a comprehensive search for the stable structures of stoichiometric (WS) nano-clusters (n = 1 - 9), within three different exchange-correlation functionals. Our results suggest that n = 5 and 8 are possible candidates for the low temperature magic sizes of WS nano-clusters while at temperatures above 500 Kelvin, n = 7 exhibits a comparable relative stability with n = 8. The electronic properties and energy gap of the lowest energy isomers were computed within several schemes, including semilocal Perdew-Burke-Ernzerhof and Becke-Lee-Yang-Parr functionals, hybrid B3LYP functional, many body based DFT+GW approach, ΔSCF method, and time dependent DFT calculations. Vibrational spectra of the lowest lying isomers, computed by the force constant method, are used to address IR spectra and thermal free energy of the clusters. Time dependent density functional calculation in a real time domain is applied to determine the full absorption spectra and optical gap of the lowest energy isomers of the WS nano-clusters.

First-principles study of MoS2 and MoSe2 nanoclusters in the framework of evolutionary algorithm and density functional theory

“…This results reflects the importance role of transition met-als in determining the stable geometry of TMDCs nanoclusters. We also noticed that, WS 2 nanoclusters exhibit less tendency to planner configurations, because even at larger sizes, WS 2 nanoclusters are not quite planner 60 .…”

“…It is already observed that nanoclusters of a nonmagnetic material may exhibit magnetism 41,60 . In order to find the stable magnetic state of the clusters, their total energy were minimized by considering different initial magnetization and then the lowest energy state was reported as the stable magnetic state.…”

Unsupervised Exploration of MoS2 Nanocluster Configurations: Structures, Energetics, and Electronic Properties

“…It is also noteworthy that we find several structures predicted using an evolutionary algorithm on WS 2 . 23 In addition we found several motifs (Figure 6) shared by many of the stable structures (indicated by colored squares in Figures 2−5): a Mo-centered tetrahedron with S atoms on the edges, a ″core″ of three or four Mo atoms bonded to each other and capped with sulfur atoms, and finally, an S-capped five-membered rings composed of two nonbonded S atoms and three Mo atoms.…”

“…Consequently, this has been the focus of a number of experimental 10,11 and theoretical studies. [12][13][14][15][16][17][18][19][20][21][22][23][24]24,25 In some cases, W n S m and W n O m clusters have been studied in parallel with Mo n S m 12,14 due to the chemical similarity between the corresponding metals and chalcogens. Investigating different stoichiometries and cluster sizes provided indeed useful information: so called "magic clusters" seem to indicate a tendency to favor over-saturation in sulfur and monolayer-like structures with growing size, rather than 3D arrangements.…”

“…[26][27][28] In this respect, two recent studies used evolutionary algorithms to explore the configuration space of MoS 2 25 (although the search was supplemented in this case by arbitrary humanprovided structures ex post) and WS 2 clusters. 24 In this work we propose an alternative sampling strategy, based on ab-initio MD simulations, accelerated with metadynamics. 29 Finite-temperature enhanced sampling approaches have become widespread as they allow to explore generic transformation mechanisms in chemistry, physics and biology, irrespective of the height of free-energy barriers.…”