Theoretical model for ultracold molecule formation via adaptive feedback control

We investigate pump-dump photoassociation of ultracold molecules with amplitude- and phase-modulated femtosecond laser pulses. For this purpose a perturbative model for the light-matter interaction is developed and combined with a genetic algorithm for adaptive feedback control of the laser pulse shapes. The model is applied to the formation of 85Rb2 molecules in a magneto-optical trap. We find for optimized pulse shapes an improvement for the formation of ground state molecules by more than a factor of 10 compared to unshaped pulses at the same pump-dump delay time, and by 40% compared to unshaped pulses at the respective optimal pump-dump delay time. Since our model yields directly the spectral amplitudes and phases of the optimized pulses, the results are directly applicable in pulse shaping experiments

Nucleation of a sodium droplet on C60

We investigate theoretically the progressive coating of C60 by several sodium atoms. Density functional calculations using a nonlocal functional are performed for NaC60 and Na2C60 in various configurations. These data are used to construct an empirical atomistic model in order to treat larger sizes in a statistical and dynamical context. Fluctuating charges are incorporated to account for charge transfer between sodium and carbon atoms. By performing systematic global optimization in the size range 1<=n<=30, we find that Na_nC60 is homogeneously coated at small sizes, and that a growing droplet is formed above n=>8. The separate effects of single ionization and thermalization are also considered, as well as the changes due to a strong external electric field. The present results are discussed in the light of various experimental data.Comment: 17 pages, 10 figure

Structure and properties of small sodium clusters

We have investigated structure and properties of small metal clusters using all-electron ab initio theoretical methods based on the Hartree-Fock approximation and density functional theory, perturbation theory and compared results of our calculations with the available experimental data and the results of other theoretical works. We have systematically calculated the optimized geometries of neutral and singly charged sodium clusters having up to 20 atoms, their multipole moments (dipole and quadrupole), static polarizabilities, binding energies per atom, ionization potentials and frequencies of normal vibration modes. Our calculations demonstrate the great role of many-electron correlations in the formation of electronic and ionic structure of small metal clusters and form a good basis for further detailed study of their dynamic properties, as well as structure and properties of other atomic cluster systems.Comment: 47 pages, 16 figure

Ab initio studies of structures and properties of small potassium clusters

We have studied the structure and properties of potassium clusters containing even number of atoms ranging from 2 to 20 at the ab initio level. The geometry optimization calculations are performed using all-electron density functional theory with gradient corrected exchange-correlation functional. Using these optimized geometries we investigate the evolution of binding energy, ionization potential, and static polarizability with the increasing size of the clusters. The polarizabilities are calculated by employing Moller-Plesset perturbation theory and time dependent density functional theory. The polarizabilities of dimer and tetramer are also calculated by employing large basis set coupled cluster theory with single and double excitations and perturbative triple excitations. The time dependent density functional theory calculations of polarizabilities are carried out with two different exchange-correlation potentials: (i) an asymptotically correct model potential and (ii) within the local density approximation. A systematic comparison with the other available theoretical and experimental data for various properties of small potassium clusters mentioned above has been performed. These comparisons reveal that both the binding energy and the ionization potential obtained with gradient corrected potential match quite well with the already published data. Similarly, the polarizabilities obtained with Moller-Plesset perturbation theory and with model potential are quite close to each other and also close to experimental data.Comment: 33 pages including 10 figure

Molecular picture of excited states and fragmentation paths of the Na

The stability against fragmentation and possible relaxation of the lowest excited states of the Na5F4 cluster (representative of cubic non stoechiometric clusters with an excess sodium atom, also called sodium-tail) is investigated by means of one-electron pseudopotential calculations with particular reference to photoabsorption processes from the ground state. Whereas the equilibrium configuration of the ground state has C3v symmetry, the doubly degenerate 12E excited state is affected by a conical intersection and a Jahn-Teller effect associated with the rotation of the sodium tail around the C3-axis. This yields a "Mexican hat" topology for the lowest sheet with three equivalent Cs minima. Alternatively the 22A1 state has a minimum retaining the C3v symmetry. The dissociation paths of the cluster along the C3-axis into respectively Na4F4 + Na and Na4F3 + NaF are also investigated. Among the former paths, the excited states are found adiabatically stable with respect to the products. However in the A1 symmetry, fragmentation into NaF exhibits an interesting avoided crossing between configurations correlated respectively with Na4F3 + + NaF- and Na4F3 + NaF. Such interaction, similar to the well-known charge exchange processes in elementary molecules might induce non adiabatic predissociation of the 22A1 state. This mechanism is invoked to explain the differences between R2PI and depletion spectra, correlated with the dissociation or relaxation of the excited states

Interaction entre calcul quantique des courbes de potentiel et expériences pour l’interprétation et la reconstitution des profils de raies : le cas de l’excimère de l’argon

La complexité des courbes de potentiel moléculaires rend souvent difficile l’interprétation fine des résultats d’études spectroscopiques expérimentales. Cet article analyse ces difficultés sur l’exemple de l’excimère [math] et examine les conditions dans lesquelles le calcul théorique peut apporter des réponses fiables aux questions en suspens : une représentation générale des critères gouvernant la précision théorique des calculs de potentiels est donnée et la détermination ou la simulation d’observables expérimentales (niveaux vibrationnels, profils de raies) permet d’amorcer un bilan des possibilités théoriques à l’heure actuelle (potentiels et modèles dynamiques) et des interactions souhaitables entre théorie et expérience

Calcul théorique en couplage Λ-Σ du spectre électronique des excimères Ar2 et Kr2 corrélé aux configurations atomiques np5(n + 1) s et np5( n + 1) p

Adiabatic potential curves for Ar (3p6 1S0) + Ar* (3p5 4s, 3p5 4p) and Kr(4p6 1 S0) + Kr* (4p5 5s, 4p5 5p) are determined in the Λ representation, from ab initio CI calculations using non-empirical pseudopotentials and extensive orbital basis sets. Avoided crossings with states correlated to higher excited configurations, e.g. 5s, 5p and 3d for Ar*2 and 6s, 6p and 4d for Kr*2 are also taken into account. The structure of the electronic spectrum of both excimers is interpreted; analysing the nature of the Rydberg MO's and the multiconfigurational wave-functions makes possible the understanding of the character of avoided crossing between Rydberg states of homonuclear rare gases.Les courbes de potentiel adiabatiques de Ar(3p6 1S 0) + Ar* (3p5 4s, 3p5 4p) et de Kr (4p6 1S0) + Kr* (4p5 5s, 4p5 5p) sont déterminées en représentation Λ, par des calculs d'IC ab initio mettant en oeuvre des pseudopotentiels non empiriques et utilisant des bases d'orbitales étendues. Les croisements évités, avec des états corrélés à des configurations plus excitées, plus précisément 5s, 5p et 3d pour Ar*2, 6s, 6p et 4d pour Kr* 2 sont également pris en compte. L'analyse de la nature des OM Rydberg et des fonctions d'onde multiconfigurationnelles permet d'interpréter la structure du spectre électronique de ces deux excimères et de comprendre le caractère des croisements évités entre états Rydberg des gaz rares homonucléaires

A pseudopotential study of molecular spectroscopy in rare gas matrices: absorption of NO in argon

We present a pseudopotential method to study the absorption spectroscopy of NO in an argon matrix modeled by a large albeit finite cluster. The excited states of NO are described with the virtual orbitals of a NO+ Hartree-Fock calculation plus a core-polarization operator to account for the electron-NO+ correlation. The argon atoms of the matrix are replaced by pseudopotentials for the repulsive contributions and core-polarization operators to account for matrix polarization and correlation with the excited electron. The model is shown to account for the matrix-induced transition shifts and also for the cut-off of the Rydberg series for n > 3 reported in absorption experiments from the ground state