Guy Makov

On the ionization potential of small metal and dielectric particles

The ionization potential of small metal and dielectric spheres is considered in different frameworks: classical, semiclassical, and quantum mechanical density functional approach. Classical calculations give conflicting results, and the generally accepted result for the ionization potential of a metal sphere of radius R: WI(R)=bulk work function+(3/8)q2/R is shown to be wrong, resulting from the classical image potential too close to the metal surface. Using appropriate cutoff to the image potential, the result WI(R)=bulk work function+(1/2)q2/R (previously obtained from solvation energy considerations) is recovered. Experimental results on relatively large particles are in agreement with the latter result. For very small clusters, deviations of experimental results from this classical behavior are shown by a density functional calculation to arise from quantum mechanical effects. These are first the spilloff of the electronic wave functions beyond the cluster edge and secondly from exchange and correlati...

Theoretical studies of the spectroscopy of excess electrons in water clusters

Variational calculation based on a continuum dielectric model, and numerical simulations based on the RWK2‐M water potential and on a pseudopotential for the electron–water interaction, are used to evaluate excitation energies and optical spectra for bound interior states of an excess electron in water clusters and in bulk water. Additionally, optical data for surface states are obtained from numerical simulations. The simulation approach uses adiabatic dynamics based on the quantum‐classical time‐dependent self‐consistent field (TDSCF) approximation and the fast‐Fourier transform (FFT) algorithm for solving the Schrodinger equation. Both approaches predict very weak or no cluster size dependence of the excitation spectrum for clusters that support interior solvated electron states. For an electron attached to the cluster in a surface localization mode, bound excited states exist for most nuclear configurations of clusters down to (H2O)−18, and the corresponding excitation energy is strongly shifted to th...

On the nonclassical asymptotic behavior of electronic properties in metal clusters

The ionization potential I(R) of small metal spheres (of radius R) as well as the electronic chemical potential μ(R) in such particles are considered within a three‐parameter variational local‐density‐functional calculation. The asymptotic (R→∞) deviations of I(R) and μ(R) from their bulk values behave as C/R and Cμ/R, respectively, where within the computational accuracy C+Cμ=0.5. These results are quantitatively similar to those obtained from a recent variational calculation by Engel and Perdew (EP), and identify the origin of the deviation of C from its classical value of 0.5 in the size dependence of μ(R). While EP show that this size dependence originates from the gradient terms in the energy functional, we find that its magnitude results from a delicate balance between different contributions. The classical limit C=0.5 is approached when both Z and R are large, where Z is the number of electrons involved in the transition. These results also lead to the resolution of an apparent paradox recently des...

Cross Slip in Cu - A Molecular Dynamics Study

The annihilations of screw dislocation dipoles via cross-slip in Cu were simulated using constant-temperature constant-stress molecular dynamics. The cross-slip mechanism and annihilation process of flexible dislocations in a large dipole configuration was identified as a dynamic variant of the Friedel-Escaig mechanism. The cross-slip rate was found to exhibit exponential dependence on the temperature, from which the activation enthalpy for the cross-slip process was calculated by the Arrhenius relation.