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The main result emerged from this calculation is that the TDDFT method is suitable for treatment of excited states of Ag clusters. The choice of specific functionals and basis sets to be used in some cases induces important effects on the calculated spectra. It is also noteworthy to mention that for some clusters, the neutral Ag6 for instance, the effect of noble gas environment is significant, while for some others such as the neutral Ag8, it is not. | Vietnam Journal of Science and Technology 55 (6A) (2017) 72-82 ABSORPTION OF SOME SMALL SILVER CLUSTERS: DFT AND CASPT2 CALCULATIONS Ngo Tuan Cuong1, * Nguyen Thanh Tung2, Nguyen Minh Tam3 1 Center for Computational Science, Hanoi National University of Education, 136 Xuan Thuy, Cau Giay, Ha Noi 2 Institute of Material Science, VAST, 18 Hoang Quoc Viet, Cau Giay, Ha Noi 3 Computational Chemistry Research Group, Ton Duc Thang University, 19 Nguyen Huu Tho, Tan Hung, District 7, Ho Chi Minh City * Email: cuongnt@hnue.edu.vn Received : 15 June 2017; Accepted for publication : 21 December 2017 ABSTRACT Two quantum chemical methods which are the time-dependent density functional theory (TD-DFT) and the complete active space CASPT2/CASSCF have been used in modeling absorption spectra of silver clusters Agn (n = 2, 3, 4, 6, 8). There is an overall good agreement between TD-DFT and CASPT2 results for transition energies. The absorption spectra of the Ag n clusters examined can reasonably be simulated using the excitation energies obtained by either TD-DFT or CASPT2 method. The main result emerged from this calculation is that the TDDFT method is suitable for treatment of excited states of Ag clusters. The choice of specific functionals and basis sets to be used in some cases induces important effects on the calculated spectra. It is also noteworthy to mention that for some clusters, the neutral Ag6 for instance, the effect of noble gas environment is significant, while for some others such as the neutral Ag8, it is not. Therefore, carrying out TD-DFT calculations to reproduce and to assign a given structure to an experimental absorption spectrum of a silver cluster, it is not only to select suitable functionals but also to take enough effects of environments into account. Keywords: silver clusters, absorptionspectra, TD-DFT computations, CASSCF/CASCASPT2. 1. INTRODUCTION Clusters of silver atom and ions have recently attracted the interest of scientists because .
