Search results for "Chemical physics"
showing 10 items of 2553 documents
On the ‘expanded local mode’ approach applied to the methane molecule: isotopic substitution CH2D2←CH4
2011
On the basis of a compilation of the ‘expanded local mode’ model and the general isotopic substitution theory, sets of simple analytical relations between different spectroscopic parameters (harmonic frequencies, ωλ, anharmonic coefficients, x λμ, ro-vibrational coefficients, , different kinds of Fermi- and Coriolis-type interaction parameters) of the CH2D2 molecule are derived. All of them are expressed as simple functions of a few initial spectroscopic parameters of the mother, CH4, molecule. Test calculations with the derived isotopic relations show that, in spite of a total absence of initial information about the CH2D2 species, the numerical results of the calculations have a very good…
Structural, electronic and energetic effects in heterocyclic fluorene derivatives fused with a fulvene unit
2019
Abstract A set of 36 heterocyclic (B, N and O) fluorene (C) derivatives fused in nine ways with fulvene ring have been analyzed by means of different local aromaticity criteria. Molecular geometry of analyzed compounds were optimized at B3LYP/6-311++G(2d,2p) level of theory. The evaluation of the local aromaticity has been carried out through the use of the geometry-based harmonic oscillator model of aromaticity (HOMA) and the magnetism-based zz‐component of the nucleus independent chemical shifts calculated 1 A above the ring center (NICS1zz) indices as well as one aromaticity index derived from the Quantum Theory Atoms in Molecules (QTAIM), i.e. the para-delocalization index (PDI). Additi…
Coupled-Cluster study of ‘no-pair’ bonding in the tetrahedral Cu4 cluster
2011
Abstract Ab initio Coupled-Cluster calculations with single and double excitations and perturbative correction to the triple, CCSD(T), have been carried out for the high-spin electronic state, ( 5 A 2 ) , of the copper cluster Cu 4 in its tetrahedral arrangement. Like alkali metals clusters, tetrahedral Cu 4 presents a bound quintet state, i.e., a situation where all the valence electrons are unpaired. This rather exotic wavefunction, also known as no-pair bonding state, is examined in detail. The influence of the basis set is also analyzed, as well as the importance of the core correlation and the effect of the basis-set superposition errors.
Towards highly accurate ab initio thermochemistry of larger systems: benzene.
2011
The high accuracy extrapolated ab initio thermochemistry (HEAT) protocol is applied to compute the total atomization energy (TAE) and the heat of formation of benzene. Large-scale coupled-cluster calculations with more than 1500 basis functions and 42 correlated electrons as well as zero-point energies based on full cubic and (semi)diagonal quartic force fields obtained with the coupled-cluster singles and doubles with perturbative treatment of the triples method and atomic natural orbital (ANO) triple- and quadruple-zeta basis sets are presented. The performance of modifications to the HEAT scheme and the scaling properties of its contributions with respect to the system size are investiga…
The ensemble switch method and related approaches to obtain interfacial free energies between coexisting phases from simulations: a brief review
2015
The accurate estimation of the excess free energy due to an interface between coexisting phases of a model system by computer simulation often is a challenging task. We review here two methods, whi...
Theoretical investigation of the potential energy surface of the van der Waals complex CH4-N-2
2009
International audience; The interaction potential energy surface of the van der Waals CH4-N-2 complex has been calculated for a broad range of intermolecular separations and configurations in the approximation of rigid interacting molecules at the CCSD(T) and MP2 levels of theory using the correlation consistent aug-cc-pVTZ basis set. The BSSE correction was taken into account for all the calculations. The most stable configurations of the complex were found. Binding energies were calculated in the CBS limit with accounting for the molecular deformations. The harmonic and anharmonic fundamental vibrational frequencies and rotational constants for the ground and first excited vibrational sta…
Multiple vibrational resonances in the Raman spectra of liquid ethanes
1990
The Raman spectra of liquid ethane, ethane-d3 and ethane-d6 were recorded and analysed. The CH3 and CD3 stretching regions were computer resolved using Cauchy-Gaussian and Voigt functions to account for asymmetric band shapes. Multiple vibrational resonances were investigated using the wavenumbers and observed intensities in these regions. The developed basis functions show strong mixing of the levels in these regions. In general the resonances appear to be less strong in the liquid phase than reported in previous studies of the gaseous state. Some new assignments in the liquid-state spectra of ethanes could be suggested.
Laser control in open molecular systems: STIRAP and Optimal Control
2007
We examine the effect of dissipation on the laser control of a process that transforms a state into a superposed state. We consider a two-dimensional double well of a single potential energy surface. In the context of reactivity, the objective of the control is the localization in a given well, for instance the creation of an enantiomeric form whereas for quantum gates, this control corresponds to one of the transformation of the Hadamard gate. The environment is either modelled by coupling few harmonic oscillators (up to five) to the system or by an effective interaction with an Ohmic bath. In the discrete case, dynamics is carried out exactly by using the coupled harmonic adiabatic channe…
Fourier-transform spectroscopy and deperturbation analysis of the spin-orbit coupled A(1)Σ(+) and b(3)Π states of KRb.
2016
Fourier-transform A(1)Σ(+) - b(3)Π → X(1)Σ(+) laser-induced fluorescence spectra were recorded for the natural mixture of (39,41)K(85,87)Rb isotopologues produced in a heatpipe oven. Overall 4200 rovibronic term values of the spin-orbit coupled A(1)Σ(+) and b(3)Π states were determined with an uncertainty of about 0.01 cm(-1) in the energy range [10 850, 14 200] cm(-1) covering rotational quantum numbers J' ∈ [3, 280]. Direct deperturbation analysis of the A ∼ b complex performed within the framework of the A(1)Σ(+) ∼ b(3)ΠΩ=0,1,2 coupled-channel approach reproduced experimental data with a standard deviation of 0.004 cm(-1). Initial parameters of the internuclear potentials and spin-orbit …
Communication: multireference equation of motion coupled cluster: a transform and diagonalize approach to electronic structure.
2014
The novel multireference equation-of-motion coupled-cluster (MREOM-CC) approaches provide versatile and accurate access to a large number of electronic states. The methods proceed by a sequence of many-body similarity transformations and a subsequent diagonalization of the transformed Hamiltonian over a compact subspace. The transformed Hamiltonian is a connected entity and preserves spin- and spatial symmetry properties of the original Hamiltonian, but is no longer Hermitean. The final diagonalization spaces are defined in terms of a complete active space (CAS) and limited excitations (1h, 1p, 2h, …) out of the CAS. The methods are invariant to rotations of orbitals within their respective…