Patrizia Calaminici

Density functional theory optimized basis sets for gradient corrected functionals: 3d transition metal systems

Density functional theory optimized basis sets for gradient corrected functionals for 3d transition metal atoms are presented. Double zeta valence polarization and triple zeta valence polarization basis sets are optimized with the PW86 functional. The performance of the newly optimized basis sets is tested in atomic and molecular calculations. Excitation energies of 3d transition metal atoms, as well as electronic configurations, structural parameters, dissociation energies, and harmonic vibrational frequencies of a large number of molecules containing 3d transition metal elements, are presented. The obtained results are compared with available experimental data as well as with other theoretical data from the literature.

Structure and stability of small copper clusters

The structure and stability of small copper clusters with up to ten atoms has been determined both for the neutral and the ionic clusters with density functional calculations. The calculations were of all-electron type. The structure optimization and frequency analysis were performed on the local density approximation level with the exchange correlation functional by Vosko, Wilk, and Nusair. Subsequently improved calculations for the stability were based on the generalized gradient approximation, where the exchange correlation functional of Perdew and Wang was used. Finally, the binding energies, ionization potentials, electron affinities, and separation energies were calculated. The results show that the trends are in agreement with available experimental data.

Density functional calculations of molecular polarizabilities and hyperpolarizabilities

This paper presents dipole moments, static polarizabilities, first hyperpolarizabilities and second hyperpolarizabilities calculated in the framework of density functional theory. All calculations have been performed using a finite field approach implemented in our new density functional theory program ALLCHEM. The calculations were of all-electron type. Both local and gradient-corrected functionals have been used. The influence of first- and second-order field-induced polarization functions, the external field strength, the numerical integration technique and the exchange-correlation functionals on the calculation of polarizabilities and hyperpolarizabilities is discussed in detail. A systematic study including 23 small and medium size molecules demonstrates that the obtained polarizabilities as well as the first and second hyperpolarizabilities are in good qualitative agreement with experimental data. The described density functional method provides polarizabilities and hyperpolarizabilities considerabl...

A density functional study of small copper clusters: Cun (n⩽5)

Density functional calculations have been performed for small copper clusters, Cun (n≤5), using the linear combination of Gaussian‐type orbitals density functional theory (LCGTO‐DFT) approach. The calculations were of the all‐electron type and local and nonlocal functionals were used. For each case, of both neutral and charged systems, several isomers have been considered in order to determine the lowest energy structures. The Jahn–Teller effect in Cu3 and Cu4 has been examined in detail. Bond lengths, equilibrium geometries, harmonic frequencies, adiabatic and vertical ionization potentials, adiabatic electron affinities, and binding energies are in reasonable agreement with experimental data, as well as with other theoretical results.

Calculation of macroscopic linear and nonlinear optical susceptibilities for the naphthalene, anthracene and meta-nitroaniline crystals

The macroscopic first- to third-order susceptibilities of naphthalene, anthracene and meta-nitroaniline (mNA) are calculated using a rigorous local field approach. Molecular (hyper)polarizabilities used as input are determined by density functional theory calculations with specially designed basis sets and for mNA also by MP2 calculations with the 6-31++G** basis set. In the case of mNA, the permanent electric local field due to the surrounding dipoles in the crystal is taken into account for the first- and second-order susceptibility by a self-consistent approach. The molecular dipole moment and first hyperpolarizability of mNA are drastically changed by the permanent local field. In all cases the calculated first-order susceptibility compares very favorably with experimental data, if the molecular response is distributed over all heavy atoms in the molecules. Similarly, the calculated second-order susceptibility for mNA is in good agreement with available experimental data, if the same distribution scheme is used and the permanent local field is taken into account properly. This implies that accurate values for the molecular second-order hyperpolarizability c have to be available. The anisotropic Lorentz field factor approximation yields results that are only slightly worse than the best ones of the rigorous local field theory for the first-order susceptibilities, but fails for the second-order susceptibility of mNA, due to its incapability to describe the large eAect of the permanent local field on the first-order hyperpolarizability b. ” 2000 Elsevier Science B.V. All rights reserved.

Comparison of static polarizabilities of Cun,Nan, and Lin(n⩽9) clusters

This paper presents the first study of static polarizabilities and polarizability anisotropies of copper clusters up to nine atoms calculated in the framework of density functional theory. The calculations were of all-electron type and have been performed by using a finite field approach implemented in the density functional program ALLCHEM. A newly developed first-order field induced copper basis set for density functional calculation was employed. A gradient-corrected exchange-correlation functional has been used. All cluster structures were fully optimized. The calculated polarizabilities of copper clusters are compared with experimental polarizabilities of sodium and lithium clusters. This comparison shows that the size dependency of the static polarizabilities per atom of copper clusters posseses the same trend as that observed in sodium clusters. However, the absolute polarizabilities of the copper clusters are considerably smaller as those of the sodium clusters.

On the Ground State of Pd13

First-principles electronic structure calculations within a gradient corrected density functional formalism have been carried out to investigate the electronic structure and magnetic properties of Pd(13) clusters. It is shown that a bilayer ground-state structure that can be regarded as a relaxed bulk fragment is most compatible with the experimental results from Stern-Gerlach measurements. An icosahedral structure, considered to be the ground state in numerous previous studies, is shown to be around 0.14 eV above the ground state. A detailed analysis of the molecular orbitals reveals the near degeneracy of the bilayer or icosahedral structures is rooted in the stabilization by p- or d-like cluster orbitals. The importance of low-lying spin states in controlling the electronic and magnetic properties of the cluster is highlighted.

V3: Structure and vibrations from density functional theory, Franck–Condon factors, and the pulsed-field ionization zero-electron-kinetic energy spectrum

Density functional calculations of neutral and cationic vanadium trimers are presented. The all-electron calculations employed a gradient-corrected exchange-correlation functional and a newly developed vanadium basis set optimized for gradient-corrected density functional calculations. For both neutral and charged systems, different isomers were studied in order to determine the lowest energy structures. A vibrational analysis was performed in order to characterize these isomers. We found an equilateral triangle 2A1′ ground state for V3 and an equilateral triangle 3A2′ ground state for V3+. The experimental pulsed-field ionization zero-electron-kinetic energy spectrum was simulated by calculating multidimensional Franck–Condon factors, using the geometries and harmonic frequencies of the calculated minima of V3 and V3+. The excellent agreement between the experimental and theoretical spectra allows the unequivocal determination of the ground state structure of V3. This work provides a final answer to the ...

Static polarizabilities of Nan (n⩽9) clusters: An all-electron density functional study

This paper presents static polarizabilities and polarizability anisotropies of sodium clusters up to nine atoms calculated in the framework of density functional theory. The calculations of the static polarizabilities and polarizability anisotropies have been performed using a finite field approach implemented in the density functional program ALLCHEM. The calculations were of the all-electron type. Local and gradient-corrected exchange-correlation functionals have been used. All molecular geometries were fully optimized at both levels of theory. A vibrational analysis was performed in order to discriminate between minima and transition state structures on the potential energy surfaces. Equilibrium geometries, bond distances, harmonic frequencies, static polarizabilities, and polarizability anisotropies for sodium clusters up to the nonamer are presented. The obtained results are compared with experimental data as well as with other theoretical results. The calculated and experimental polarizabilities are...

Assessment of density functional theory optimized basis sets for gradient corrected functionals to transition metal systems: The case of small Nin (n⩽5) clusters

Density functional calculations have been performed for small nickel clusters, Ni(n), Ni(n) (+), and Ni(n)(-) (n<or=5), using the linear combination of Gaussian-type orbital density functional theory approach. Newly developed nickel all-electron basis sets optimized for generalized gradient approximation (GGA) as well as an all-electron basis set optimized for the local density approximation were employed. For both neutral and charged systems, several isomers and different multiplicities were studied in order to determine the lowest energy structures. A vibrational analysis was performed in order to characterize these isomers. Structural parameters, harmonic frequencies, binding energies, ionization potentials, and electron affinities are reported. This work shows that the employed GGA basis sets for the nickel atom are important for the correct prediction of the ground state structures of small nickel clusters and that the structural assignment of these systems can be performed, with a good resolution, over the ionization potential.