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We have implemented the polarizable continuum model for solute–solvent interactions into a plane-wave (PW) Car–Parrinello code. A comparison between PW and Gaussian-type orbitals (GTO) basis sets implementations, concerning solvation energies and dipole moments of a number of small systems, is reported. All the computations have been performed using the BPW91 exchange-correlation functional. GTO calculation has been performed using the 6-311G(d,p) basis set for geometry optimizations, and the aug-cc-pVTZ basis for energies and dipole moments. PW calculations were carried out on the Gaussian optimized geometries, up to an energy cutoff of 30 Ry. Excellent agreement between PW and GTO calculations is obtained, with average deviations of solute–solvent interaction energies lower than 0.5 kcal/mol.

The acid–base chemistry of luteolin, a flavonoid with important pharmacological and dyeing properties, and of the related methyl ether derivatives have been investigated by DFT and MP2 methods, testing different computational setups. We calculate the p K a ’s of all the possible deprotonation sites, for which no experimental assignment could be achieved. The calculated p K a ’s deliver a different acidity order for the two most acidic deprotonation sites between luteolin and its methyl ether derivatives, due to intramolecular hydrogen bonding in luteolin. A lowest pKa of 6.19 is computed for luteolin, in good agreement with available experimental data.

We report a theoretical investigation of β-elimination reactions in systems activated by the pyridine ring. The investigated reaction, the acetohydroxamate-induced β-elimination in protonated N-[2-(2-pyridyl)ethyl]quinuclidinium, offers a unique opportunity to test computational methodologies since detailed kinetic experimental data are available. We calculated the pKas of the acetohydroxamic acid and the substrate and thoroughly characterized the reactive free-energy profile. The reaction proceeds via a stable carbanion intermediate. Except a discrepancy in the reproduction of the pKa of the acetohydroxamic acid, the calculated free-energy profile is in excellent agreement with the experiment, showing the general reliability of the present approach.

We report time-dependent (TD) and coupled-perturbed (CP) DFT/HF investigations, on the linear and non-linear optical properties of M(II)-complexes of [5-[(4′-dimethylaminophenyl)-ethynyl]-15-[(4″-nitrophenyl)ethynyl]-10,20-diphenylporphyrin], with M = Zn, Cu, Ni. The TD-DFT absorption spectrum is in good agreement with the experimental one, allowing us to identify the transitions mainly responsible of the NLO response. CP-DFT/CP-HF calculations provide similar hyperpolarizability values for the three complexes, suggesting an irrelevant role of the metal center. A sharp hyperpolarizability increase is calculated at an incident laser wavelength of 1.064 μm compared to 1.907 μm, which seems to be responsible for the large differences between Zn, Cu and Ni complexes reported experimentally.

Density functional calculations are carried out on the Cu5(C6H5)5, Ag4(C6H5)4 and Au5(C6H5)5 systems. Electronic structure and bonding aspects of the interaction between the Mn and (C6H5)n units are investigated. Calculations are performed on the corresponding naked clusters of four and five metal atoms in order to study the M-M bond and the stability trend as a function of cluster size. The following conclusions are reached: (i) M-M bonding is present in all the complexes (both naked and with phenyls) and (ii) the stability increases with cluster size, even if, for the complexes with phenyls, tetramers and pentamers show a comparable stability. Relativistic effects turn out to be essential for the description of gold systems but not remarkable for silver and copper clusters.

”Ab initio“ calculations have been performed on the systems NiN 2 and Ni(PH 3 ) 2 N 2 to investigate the relative stability of end-on and side-on coordination of dinitrogen to Ni 0 . The results indicate that both the π-back-donation and the reduction in the σ repulsion are important factors in the description of the NiN 2 bonding. In NiN 2 , it is possible to reduce efficiently the repulsion by 4s polarization and the dinitrogen can come close enough to nickel in order to reach overlap in the π space for end-on coordination: this favors the end-on bonding with respect to the side-on one. When ligands are present on both sides of nickel, 4s polarization is no loger possible and N 2 cannot come close enough to nickel to allow the best overlap: this disfavors mainly the end-on coordination where a shorter r (NiN) is required and explains the preference for side-on coordination in Ni(PH 3 ) 2 N 2 .

Multiple scattering Xα calculations with overlapping spheres were performed on CH3F and CH2F2 for all-valence region ionization potentials. Comparison with previous Xα calculations shows a substantial improvement.

Extensive CI calculations have been earned out on the ground and singly ionized states of BeH 2 . Geometry optimization has been performed for all the states studied, together with the computation of harmonic force constants. Green's function calculations of the vertical ionization potentials show excellent agreement with the CI results.

A Green's function study and an (e,2e) spectroscopic investigation have been carried out on the C 2 H 3 Cl and C 2 H 3 Br molecules. The complete valence ionization spectra of both molecules are discussed. An analysis of the experimental and theoretical electron momentum distributions is also presented, allowing an unambiguous assignment of the spectral features.

A Green's function study has been performed on CHF3 and CF4. Theoretical results are compared with (e 2e) spectral data. Previous assignment of valence-shell orbitals is confirmed and a splitting of the innermost ionizations over many shake-up terms in experimental and theoretical results on both molecules.

Individual orbital contributions to the total relaxation energies accompanying core ionizations in carbon monoxide have been computed within the ΔSCF formalism. The magnitude and sign of the contributions are shown to depend quite markedly on the localization and bonding characteristics of the orbitals concerned and vary quite significantly with bond length.

A Green's function study and an (e,2e) spectral investigation have been performed on CH 4 and some of its fluoro derivatives. The satellite structures and the breakdown of the orbital picture for inner valence shells are discussed.

Non-empirical LCAO MO SCF calculations within the Hartree-Fock formalism have been performed on linear and bent conformations of NiCO, for both the states arising from the 3d94s1 and 3d10 electronic configurations of Ni, for ground and core ionized species. Binding and relaxation energies are computed for the nickel atom, the free ligand (CO) and the absorbed species (NiCO). Comparison with available experimental data reveals good agreement for the shifts in core binding energies for the bent, 3d94s1 NiCO system. The main contribution to these binding energy shifts is found to be due to relaxation effects, which may be rationalized in terms of atomic population and bond overlap changes accompanying core ionization.