Transition-metal clusters finite-temperature

In the third step, our ZT-TBMD method has been extended by incorporating the Nose-bath (Nose 1984) and the Multiple Histogram approximations (Fanourgakis et al. 1997), so as to be applicable to cluster studies at finite temperatures in an efficient way (Andriotis et al. 2006, 2007 Fthenakis et al. 2003). This generalization allows one to calculate the caloric curve for the cluster and use this to study the effect of temperature on the structural, electronic, and magnetic properties of transition metal clusters and binary systems containing transition metal and semiconductor atoms. The method has been used to study the variation of structural and magnetic properties with temperature as well as to obtain the caloric curves of the Ni-clusters (Andriotis et al. 2006,2007 Fthenakis et al. 2003). 

The single ground state AIMD-GDF dynamics is a useful tool to study the influence of the temperature on the structural properties of small metallic clusters allowing to find mechanisms of isomerization processes as well as to formulate precise criteria for phase transitions in finite systems... 

In Section 2.3 the structural and optical properties of neutral and cationic Na clusters at r = 0 K as functions of size are presented and compared with experimental data recorded at low temperature. The temperature-dependent line-broadening will be illustrated by the example of Na9, since in this case a comparison with experimental data at different temperatures is particularly instructive. In Section 2.4 the results of ab initio molecular dynamics (AIMD) studies on Li9 will serve to show different temperature behavior of distinct types of structures as well as their isomerization mechanisms. The study of possible metal-insulator transitions and segregation into metallic and ionic parts in finite systems carried out on prototypes of nonstoichiometric alkali halide and alkali hydride clusters with single and multiple excess electrons is presented in Section 2.5. A comparison of structural and optical characteristics of Na F and lAnUm (n > m) series allows us to illustrate the influence of different bonding properties. 

The ab initio determination of optically allowed transitions and their intensities for the most stable cluster structures is feasible in particular for simple metals (la) " as well as for mixed aggregates involving metallic, ionic, or polar bonding and combination, of these bonding types. A comparison of the theoretical predictions which are strictly valid at zero temperature with the spectra recorded at low temperature allows one to propose the assignment of the cluster structure to the measured features and to account for the specific character of small finite clusters. 

---