About Chemical Modifications of Finite Dimensional QED Models

Suggestion of modifications of finite-dimensional quantum-electrodynamic (QED) models are proposed for interpreting chemical reactions in terms of artificial atoms and molecules on quantum dots placed in optical cavities. Moving both photons and atoms is possible between the cavities. Super dark states of diatomic systems are described, in which the motion of atoms between cavities is impossible due to quantum interference. Chemical processes with two level atoms and three level atoms with lambda spectrum are schematically modeled by solving the single quantum master equation with the Lindblad operators of photon leakage from the cavity and influx into it; association and dissociation reactions then differ only in the initial states. An example is given of the optical interpretation of the transition of an electron from atom to atom in terms of the multilevel Tavis-Cummings-Hubbard model with an estimate of the accuracy. Polyatomic chemical reactions are too complex for accurate modeling. Our method of rough interpretation helps to obtain their long-term results, for example, the form of stationary states of reagents, such as dark and super dark states.

A Spectroscopic Validation of the Improved Lennard–Jones Model

The Lennard–Jones (LJ) and Improved Lennard–Jones (ILJ) potential models have been deeply tested on the most accurate CCSD(T)/CBS electronic energies calculated for some weakly bound prototype systems. These results are important to plan the correct application of such models to systems at increasing complexity. CCSD(T)/CBS ground state electronic energies were determined for 21 diatomic systems composed by the combination of the noble gas atoms. These potentials were employed to calculate the rovibrational spectroscopic constants, and the results show that for 20 of the 21 pairs the ILJ predictions agree more effectively with the experimental data than those of the LJ model. The CCSD(T)/CBS energies were also used to determine the β parameter of the ILJ form, related to the softness/hardness of the interacting partners and controlling the shape of the potential well. This information supports the experimental finding that suggests the adoption of β≈9 for most of the systems involving noble gas atoms. The He-Ne and He-Ar molecules have a lifetime of less than 1ps in the 200–500 K temperature range, indicating that they are not considered stable under thermal conditions of gaseous bulks. Furthermore, the controversy concerning the presence of a “virtual” or a “real” vibrational state in the He2 molecule is discussed.

Determinação de Constantes Espectroscópicas Rovibracionais via Monte Carlo Quântico

This work evaluated the efficiency of the Diffusion quantum Monte Carlo (DMC) method in determining potential energy curves (PECs) for diatomic systems. This evaluation was performed by determining rovibrational spectroscopic constants from PECs obtained for the HeH+ and LiH systems. The trial wave functions used are derived from the Hartree-Fock and MCSCF methods. The method used to calculate the spectroscopic constants was the Discrete Variable Representation (DVR) method. Thus, the PECs generated from the DMC produced the best results, being very close to the experimental results. Thus, the DMC method proved to be more efficient than the other methods used (MCSCF and CCSD(T)). The results obtained in this study indicate that the DMC-DVR methodology has a great potential to become a reference in the determination of spectroscopic properties.