V. Bonačić-Koutecký

Effective core potential-configuration interaction study of electronic structure and geometry of small neutral and cationic Agn clusters : predictions and interpretation of measured properties

The ground state geometries of small neutral Agn(n=2–9) and cationic Agn+ (n=2–9) clusters have been determined in the framework of the Hartree–Fock and complete active space self‐consistent field (CASSCF) procedure employing a relativistic effective core potential (RECP) accounting for core–valence correlation effects (CVC). Similarities and differences between topologies of neutral and charged structures have been found. Large scale configuration interaction (CI) calculations for 5s electrons only have been carried out for determining stabilities and ionization potentials (IP). A comparison between predicted and measured observables allows tentative geometrical assignments. Structural and electronic properties of small Ia and Ib clusters are compared.

Evolution of the electronic structure of lithium clusters between four and eight atoms

Absorption spectra of lithium clusters containing four to eight atoms have been measured using depletion spectroscopy. Few intense transitions are observed, always located in two predominant spectral regions, ∼480 and 680 nm. The spectra are interpreted using ab initio configuration interaction (CI) calculations, leading to a complete characterization of the excited states and a straightforward determination of the ground state geometrical structure. Intense transitions are explained by interference effects in the transition amplitude and symmetry considerations. Comparisons with semiclassical models, in which an effective mass correction is introduced, are also presented.

Theoretical interpretation of the photoelectron detachment spectra of Na−2–5 and of the absorption spectra of Na3, Na4, and Na8 clusters

The configuration‐interaction (CI) study of excited states of alkali metal clusters accounts for spectroscopical patterns obtained from (i) the photoelectron detachment spectra of their anions and from (ii) the photodepletion spectra of the neutral species, reproduces observed excitation energies, intensities for allowed transitions, and permits an assignment of cluster structures. For Na−2–4 the linear anionic geometries are responsible for the photoelectron detachment spectra. In the case of Na−5, both planar and linear anionic isomers seem to contribute to the recorded spectrum. The calculation of optically allowed states for Na3(C2v) and Na4(D2h) structures and oscillator strengths yield rich spectra which have been fully assigned to the observed ones. In the case of Na8, the Td and the related D2d forms give rise to an intense transition located at ∼495 nm and the weak fine structure shifted to the red in full agreement with the measured spectrum. A molecular versus collective excitation interpretati...

Effective core potential‐configuration interaction study of electronic structure and geometry of small anionic Agn clusters: Predictions and interpretation of photodetachment spectra

The ground state geometries of small anionic Ag−n(n=2–9) clusters were determined in the framework of the Hartree–Fock procedure employing a relativistic effective core potential (RECP) accounting for core–valence correlation (CVC) effects. Large scale configuration interaction (CI) calculations for 5s electrons only were carried out in order to determine the ground state energies of anionic and neutral species as well as of excited states of the latter in the geometries of the former. The calculated vertical detachment and excitation energies account for the observed photodetachment spectroscopic patterns and permit an assignment of the cluster geometries. Structural and electronic properties of small Ia and Ib anionic clusters are compared.

Quantum molecular interpretation of the absorption spectra of Na5, Na6, and Na7 clusters

The configuration‐interaction study of the excited states of the most‐stable structures of Na5, Na6, and Na7 clusters employing ab initio effective‐core potential corrected by the core polarization potential predicts spectroscopic patterns which are in good agreement with the measured depletion spectra. A comparison of the transition energies and the oscillator strengths with the experimental data makes possible tentative structural assignments. Planar Na5 and Na6 structures and the three‐dimensional pentagonal bipyramid for Na7 appear responsible for the recorded spectra. The full agreement between theory and experiment is present for Na6 and Na7. The measured cross sections and calculated oscillator strengths for Na5 compare better for lower transition energies than for higher ones. A many‐electron description of the excited states of Na5, Na6, and Na7 yields a complete quantum molecular interpretation of the absorption spectra. From a comparison of the experimental and theoretical results the conclusio...

Abinitio predictions of structural and optical response properties of Na+n clusters: Interpretation of depletion spectra at low temperature

We show that a comparison of the depletion spectra of Na+n (n=2–9,11,21) clusters recorded at low temperature and optically allowed transitions determined for the stable structures using ab initio methods accounting for electron correlation allows the assignment of the cluster geometry to the measured features. Due to the large mobility of atoms in alkali metal clusters, the influence of temperature on structural and electronic properties is significant. The lowering of temperature reveals new spectroscopic features which are structure dependent. Optical response properties of small cationic Na+n clusters are characterized by rich molecularlike spectroscopic patterns, also with increasing size, and differ substantially from those found for neutral clusters. It has been clearly demonstrated that not only the number of valence electrons but its mutual interplay with the geometric properties determine optical response features.

Critically heterosymmetric biradicaloid geometries of of protonated Schiff bases

Ab initio large scale calculations confirm the existence of anS0-S1 conical intersection at orthogonally twisted double bond geometries in the protonated Schiff bases, methaniminium and propeniminium, originally predicted from the simple two-electron, two-orbital model. In the vicinity of these geometries, theS0 andS1 wavefunctions differ by a translocation of a positive charge. Several conjectures are formulated for the consequence of these results for photochemical cis-trans isomerization around double bonds in protonated Schiff bases and a possible relation to the primary step in the vision process is pointed out.

Ab initio configuration-interaction study of the photoelectron spectra of small sodium cluster anions

We find that the ab initio direct configuration‐interaction calculations on Na−2–5 and Na2–5 account for the observed patterns of photoelectron spectra, reproduce the observed excitation energies in a semiquantitative way and permit an assignment of cluster geometries.

An ab initio configuration interaction study of the excited states of the Na4 cluster: Assignment of the absorption spectrum

Abstract The vertical spectra for excited states of the Na 4 cluster in its rhombus geometry and in its distorted tetrahedron geometry have been determined by ab initio large-scale CI methods. The excitation energies of optically allowed states for the rhombic structure are in good agreement with the spectroscopic transitions obtained from optical response experiments. The results are used to make structural and electronic assignment to those spectra. The nature of the interaction among alkali metal atoms in the ground and excited states of sodium tetramers has been characterized according to the leading features of the correlated wavefunctions.

Interpretation of the absorption spectrum of Na8

Abstract The optically allowed transitions for three neutral Na 8 structures (T d , D 2d and D 4d ) and their oscillator strength have been determined using the configuration-interaction procedure. The assignment to the observed optical response spectrum exhibiting a very intense transition at 494 nm and fine structure at ≈ 590 and ≈ 730 nm has been made using the calculated spectrum of the T d and related D 2d structures. The antiprism form of Na 8 yields blue-shifted transitions with respect to the observed ones. The quantum-molecular approach has been compared with the semiclassical Mie-Drude model.