DFT studies of the structural and electronic properties of PdGe _n (n=1-11) clusters and adsorption capacity for some gas molecules

Density functional theory calculations have been employed for the theoretical studies of the geometric structures and electronic characteristics of PdGen (n = 1-11) clusters. An analysis of the second- order energy differences indicates that PdGe7 and PdGe10 clusters possess superior thermodynamic stability. PdGe10 displays the highest chemical stability and the lowest chemical activity, due to its largest energy gap value (E-g). Vertical ionization potential and vertical electron affinity exhibit the decreasing and increasing trends, respectively, with the increase of the number n of Ge atoms. PdGe10 presents the highest electronegativity among these clusters. The analysis on the adsorption properties of PdGen (n = 7,10) clusters for gas molecules (e.g. CO, NO, NO2, NH3, SO2 and H2S) yields the adsorption structures, adsorption energies, Mulliken charge transfer and the changes in the electronic properties. All the listed gas molecules chemically adsorb onto PdGe7. PdGe10 has a better adsorption performance for NO2, while its adsorption ability for CO is poorer. The potentiality of PdGen (n = 7, 10) clusters as gas sensors is also evaluated and reveals that NO adsorption significantly affects the electronic properties, especially conductivity, of the systems. PdGe10 has an appropriate NO adsorption capacity and significant charge transfer, with the adsorption energy of -0.278 eV and the recovery time of about 10(-9)s, indicating its fast response and hence good potentiality as the NO sensor. In contrast, PdGe7 has a higher adsorption capability towards NO with a lower adsorption energy of -1.16 eV, leading to the difficulty in desorption and a longer recovery time of over 12 h.