Vibrational Heat Capacity of Gold Cluster AuN=14 at Low Temperatures

The vibrational heat capacity Cvib of a re-optimized neutral gold cluster AuN=14 was investigated at temperatures 0.5-300/950 K. The vibrational frequency of a optimized cluster was revealed by small atomic displacements using a numerical finite-differentiation method. This method was implemented using density-functional tight-binding (DFTB) approach. The desired set of system eigenfrequencies (3N-6) was obtained by diagonalization of the symmetric positive semidefinite Hessian matrix. Our investigation revealed that the Cvib curve is strongly influenced by temperature, size and structure dependency. The effect of the range of interatomic forces is studied, especially the lower frequencies make a significant contribution to the heat capacity at low temperatures. Surprisingly, the Boson peaks are typically ascribed to an excess density of vibrational states for the small clusters. Finally, temperature dependencies of the vibrational heat capacities of the re-optimized neutral gold cluster have been studied for the first time.