The structure energetics and melting behavior of free platinum clusters

---

Tezin Türü: Doktora

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Fen Edebiyat Fakültesi, Fizik Bölümü, Türkiye

Tezin Onay Tarihi: 2004

Öğrenci: ALİ SEBETCİ

Danışman: HATİCE KÖKTEN

Özet:

The Voter and Chen version of an embedded-atom model, derived by fitting to experimental data of both the diatomic molecule and bulk platinum simultaneously, has been applied to study the locally stable structures, energetics, growth patterns and melting behavior of free platinum clusters in the size range of N=2-56 and N=75. Using the constant-energy molecular dynamics simulations, thermal and conjugate-gradient minimization techniques, the global minima and the other locally stable structures have been distinguished from those stationary structures that correspond to saddle points of the potential energy surface. The number of isomers and the probabilities of sampling different basins of attractions of the clusters from 2 to 22 atoms are obtained. The energy spectra of these clusters have been analyzed. The correlations between the total energy of the 75-atom cluster and the isomer number and the energy-spectrum-width of the isomers are investigated. The number of isomers of 75-atom cluster as a function of the total energy is presented, and the isomer probability distribution is discussed. The melting behavior of Pt_N clusters in the size range of N=12-14, 54-56, and N=75 has been studied. An atom-resolved analysis method including physical quantities such as the root-mean-square bond-length fluctuations and the coordination numbers for indivudual atoms as the functions of the temperature has been presented. Comparisons have been made with the results of previous calculations using electronic structure and empirical potential methods. The results show that the global minima have structures based on either octahedral, decahedral or icosahedral packing.