Narrow Results

This work is devoted to the elucidation of the applicability of the jellium model to the description of alkali cluster properties. We compare the jellium model results with those derived within ab initio theoretical approaches and with experiments. On the basis of Hartree–Fock and local-density approximations we have calculated the binding energies per atom, ionization potentials, deformation parameters and optimized values of the Wigner–Seitz radii for neutral and singly charged sodium clusters with the number of atoms N ≤ 20. The characteristics calculated within the framework of the deformed jellium model are compared with the results derived from ab initio simulations of cluster electronic and ionic structure based on density functional theory and systematic post Hartree–Fock many-body perturbation theory accounting for all electrons in the system. The comparison performed demonstrates the great role of the cluster shape deformations in the formation cluster properties and quite reasonable level of applicability of the deformed jellium model. This elucidates the similarities of atomic cluster physics with the physics of atomic nuclei.

We present a new theoretical framework for modeling the fusion process of Lennard–Jones (LJ) clusters. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system and absorbing its energy at each step, we find cluster growing paths up to the cluster size of 150 atoms. We demonstrate that in this way all known global minima structures of the LJ-clusters can be found. Our method provides an efficient tool for the calculation and analysis of atomic cluster structure. With its use we justify the magic number sequence for the clusters of noble gas atoms and compare it with experimental observations. We report the striking correspondence of the peaks in the dependence of the second derivative of the binding energy per atom on cluster size calculated for the chain of the LJ-clusters based on the icosahedral symmetry with the peaks in the abundance mass spectra experimentally measured for the clusters of noble gas atoms. Our method serves as an efficient alternative to the global optimization techniques based on the Monte-Carlo simulations and it can be applied for the solutions of a broad variety of problems in which atomic cluster structure is important.

We suggest a theoretical method based on statistical mechanics for treating the α-helix ↔ random coil transition in polypeptides. This process is considered to be a first-order-like phase transition. The developed theory is free of model parameters and is based solely on fundamental physical principles. We apply the developed formalism to the description of thermodynamical properties of alanine polypeptides of different lengths. We analyze the essential thermodynamical properties of the system, such as heat capacity, phase transition temperature, and latent heat of the phase transition. Also, we obtain the same thermodynamical characteristics from molecular dynamics simulations and compare the results with those of statistical mechanics calculations. The comparison proves the validity of the statistical mechanics approach and establishes its accuracy.

The optimized structure and electronic properties of small sodium and magnesium clusters have been investigated using ab initio theoretical methods based on density-functional theory and post-Hartree-Fock many-body perturbation theory accounting for all electrons in the system A new theoretical framework for modelling the fusion process of noble gas clusters is presented We report the striking correspondence of the peaks in the experimentally measured abundance mass spectra with the peaks in the size-dependence of the second derivative of the binding energy per atom calculated for the chain of the noble gas clusters up to 150 atoms.

We predict a strong enhancement in the photoabsorption of small Mg clusters in the region of 4-5 eV due to the resonant excitation of the plasmon oscillations of cluster electrons. The photoabsorption spectra for neutral Mg clusters consisting of up to N = 11 atoms have been calculated using ab initio framework based on the time dependent density functional theory (TDDFT). The nature of predicted resonances has been elucidated by comparison of the results of the ab initio calculations with the results of the classical Mie theory. The splitting of the plasmon resonances caused by the cluster deformation is analysed. The reliability of the used calculation scheme has been proved by performing the test calculation for a number of sodium clusters and the comparison of the results obtained with the results of other methods and experiment.

Fission of doubly charged sodium clusters is studied using the open-shell two-center deformed jellium model approximation and ab initio molecular dynamic approach accounting for all electrons in the system. Results of calculations of fission reactions and are presented. Dependence of the fission barriers on isomer structure of the parent cluster is analyzed. Importance of rearrangement of the cluster structure during the fission process is elucidated. This rearrangement may include transition to another isomer state of the parent cluster before actual separation on the daughter fragments begins and/or forming a "neck" between the separating fragments.