A dispersion-corrected DFT insight into the structural, electronic and CH4 adsorption properties of small tin-oxide clusters

Abstract

The main goal of this paper is to investigate the structural and electronic properties of small tin-oxide clusters, SnxOy (x = 2–6), before and after methane (CH4) physisorption. To this end, we employ the dispersion-corrected density functional theory (DFT-D2). At first, we demonstrate the relative binding stability of SnxOy clusters with a fixed number of tin atoms via analysis of their binding energy per atom and second-order energy differences. Our results show that the highest relative stability occurs at y = 2, y = 3, y = 4, y = 6 and y = 8 for Sn2Oy, Sn3Oy, Sn4Oy, Sn5Oy and Sn6Oy clusters, respectively. Furthermore, with the cluster size increasing, the ring-shape to cube-like structural crossover is occurred. The higher average coordination and total number of bonds in cube-like clusters make their interatomic bonds weaker and longer. On the other hand, the cube-like clusters, in comparison with ring-shape ones, possess higher chemical potential and lower chemical hardness that lead to their more chemical reactivity. We then proceed to study the CH4 adsorption properties of the resulted most stable clusters. The lowest-energy structures of CH4-adsorbed clusters have been found by comparing the adsorption energy of different configurations. It is found that Van der Waals interactions lead to exothermic physisorption of CH4 on each tin-oxide cluster with the adsorption energy ranging from −101 to −191 meV. In addition, upon CH4 adsorption on SnxOy clusters, the energy gap is decreased which shows an enhancement in the conductivity of the clusters. As a result, the CH4 physisorption ability of these small studied tin-oxide clusters provides their application feasibility as the low-temperature CH4 gas sensors.