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In the search for efficient molecular dynamics simulation models both simplicity and acceptable accuracy matter. In the present study, a model of the graphene- $$\hbox {H}_2$$ physisorption system is used to explore its performance and limitations under canonical NVT and microcanonical NVE simulation conditions. The model implies several simplifications that can be summarized in (a) a single ideal planar frozen graphene-like layer of C atoms, (b) rigid rotor $$\hbox {H}_2$$ molecules and (c) interaction potentials written as C-H and $$\hbox {H}_2$$ - $$\hbox {H}_2$$ site-site Improved Lennard-Jones potentials parameterized to reproduce DFT calculations. This model can be used in a variety of molecular dynamics simulation conditions, both in NVT and NVE ensembles. Such simulations lead to the formation of a single layer of adsorbed $$\hbox {H}_2$$ molecules in dynamically stable equilibrium with a fluid-phase region. In addition, the incipient formation of secondary layers for high-density conditions is also observed. Some properties as average pressure, temperatures and fluid-phase densities are discussed as well as possible improvements of the model. [ABSTRACT FROM AUTHOR]

In this work, the linear response formalism with a triples-corrected CCSD reference wave function, LR-CCSDR(3), is applied to the calculation of vertical excitation energies of singlet states of the FCO molecule. A basis set of atomic natural orbitals augmented with a series of Rydberg functions has been used in the calculations. A large number of electronically excited states were calculated, and the valence, Rydberg, or mixed character of the states were investigated. In addition, the molecular quantum defect orbital (MQDO) method has been used to determine transition intensities involving Rydberg states. Excitation energies and transition intensities for Rydberg states with n > 3 are reported for the first time. [ABSTRACT FROM AUTHOR]

Coupled cluster linear response formalism has been used to compute the vertical excitation energies and oscillator strengths of the lowest valence singlet states of dimethyl sulfide (DMS) and dimethyl sulphoxide (DMSO). Unless for one exception, the results are in very good agreement with experiment, but a new assignment of one DMSO transition is proposed. [ABSTRACT FROM AUTHOR]

The size-consistent self-consistent configuration interaction method, (SC)2-CI, is a procedure based on the matrix dressing formulation of the intermediate hamiltonian theory, which aims to correct the size-extensivity problem in truncated or selected configuration interaction (CI) calculations. Corrected energies and CI-like functions are obtained. In the present paper, a procedure is proposed to get size consistent mean values of properties from the (SC)2 -SR-SDCI vectors. It can be easily extended, though in a less rigorous way, to (SC)2 -MR-SDCI functions. Calculations have been performed in 13 trial systems to test the size consistency behaviour of mean value one-electron properties obtained from (SC)2 vectors and the accuracy limits of the procedure. Properties for ground and excited states have been tested in the SR-SDCI, (SC)2 -SR-SDCI, MR-SDCI, and (SC)2 -MR-SDCI approximations. The dipole and quadrupole moments of several small molecules have been calculated with the corrected (SC)2 -SR-SDCI method. The values are compared to experimental and theoretical reference values. [ABSTRACT FROM AUTHOR]