Papers by Ivana Paidarova
Chemical Physics, Dec 1, 2007
Accurate energy ab initio calculations have been performed for three lowest electronic states of ... more Accurate energy ab initio calculations have been performed for three lowest electronic states of He3+ using the internally contracted multireference configuration interaction (icMRCI) method and an augmented correlation-consistent basis set of atomic orbitals. A broad range of He3+ geometries has been considered and the calculated energies have been represented analytically. The present results are thoroughly checked in comparison with data
Chemical Physics, Feb 1, 1981
Two different modifications of the atoms-in~olecules method are applied to various states of the ... more Two different modifications of the atoms-in~olecules method are applied to various states of the HeH and HeH* species. The calculations are canied out in.3 wide range of internuclear separations in order to obtain a description of the diatomics adequate to serve as input for a subsequent DLL calculation of potential energy surfaces of fI-IeH2)C_ The remits are compared withother presently available cA&~ons.
European Physical Journal D, May 1, 2016
Abstract In this paper we present calculations of the static polarizability and its derivatives f... more Abstract In this paper we present calculations of the static polarizability and its derivatives for the adamantane molecule carried out at the density functional theory level using the B3LYP exchange-correlation functional and Sadlej’s polarized valence triple zeta basis set. It is shown that the polarizability tensor is necessary to correct long-range behavior of DFT functionals used in electron-molecule scattering calculations. The impact of such a long-range correction is demonstrated on elastic and vibrationally inelastic electron collisions with adamantane, a molecule representing a large polyatomic target for electron scattering calculations. Graphical abstract
International Journal of Quantum Chemistry, 1997
Chemical Physics, Jun 1, 1987
Non-adiabatic interaction between the He(2 3S)-H, and He(2 3P)-H, potential energy surfaces is st... more Non-adiabatic interaction between the He(2 3S)-H, and He(2 3P)-H, potential energy surfaces is studied. The potentials and non-adiabatic coupling vector are calculated by use of the hermitean version of the DIM scheme for description of polyatomic autoionizing systems. The shape and location of the non-adiabatic region are determined and used to estimate translational states of the He*-Ha collision system which lead to non-adiabatic transitions. The effect of the behaviour of the system in the non-adiabatic region on the autoionization feature of a He(2 3S)-H, collision is outlined.
Chemical Physics, May 1, 1986
A rigorous first-order perturbation scheme corresponding to the non-hermitean DIM model of resona... more A rigorous first-order perturbation scheme corresponding to the non-hermitean DIM model of resonant states of polyatomic systems is elaborated. Sample calculations on the He(23S)-H, and He(2'S)-H, systems are reported. The approach seems to be suited for use in theoretical description of the dynamics of autoionizing collision systems.
Chemical Physics, May 1, 1988
Non-adiabatic coupling between the He(2 %)-Hz and He('P)-Hz potential energy surfaces is studied.... more Non-adiabatic coupling between the He(2 %)-Hz and He('P)-Hz potential energy surfaces is studied. The potentials and nonadiabatic coupling elements are obtained by use of the Hermitean version of the diatomics-in-molecules approach to the theoretical description of polyatomic autoionizing systems. The shape and location of the region of strong non-adiabatic interaction in the He*-H, configuration space are determined and used to estimate those initial He*-Hz collision energies which can lead to breakdown of the Born-Oppenheimer approximation. The connection between the behaviour of the He(2 %)-Hz collision system in the non-adiabatic region and its lifetime is outlined.
INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2009: (ICCMSE 2009), 2012
International Journal of Quantum Chemistry, Dec 6, 1998
Wave-operator equations associated with the determination of effective Hamiltonians are generally... more Wave-operator equations associated with the determination of effective Hamiltonians are generally solved by perturbation methods. However, it is well known that for most actual systems the standard Rayleigh-Schrodinger and Brillouin-Wigner series either converge slowly or diverge. One way how to deal with this problem is to modify or to renormalize the standard wave equations. For that purpose, we derive new derivative and convergence superoperators within the two basic Rayleigh-Schrodinger and Brillouin-Wigner formalisms. Since the direct use of these superoperators would imply difficult operator inversions, we investigate the efficiency of various approximations of these superoperators. It is shown that these approximations can overcome convergence difficulties and also open the way to systematic infinite partial summation schemes. A numerical illustration is presented for a model system of N non-interacting hydrogen molecules. Finally, it is shown that the determination of regular two-component relativistic Hamiltonians is also relevant to this approach. © 1996 John Wiley & Sons, Inc.
Physical Chemistry Chemical Physics, 2000
ABSTRACT
Springer eBooks, 2003
The wave operator theory of quantum dynamics is reviewed and applied to the study of line profile... more The wave operator theory of quantum dynamics is reviewed and applied to the study of line profiles and to the determination of the dynamics of interacting resonances. New exact energy-dependent effective Hamiltonians are derived from a model Hamiltonian describing several resonances interacting with several continua. These effective Hamiltonians are especially relevant for describing and understanding the physics near the energy thresholds of decaying channels. The applications underline the relevance of investigating simultaneously spectroscopy (line profiles) and the dynamics (transition probabilities) by means of effective Hamiltonians. The physics of a discrete state coupled to a finite-width continuum is revisited. A novel model study of giant resonances is presented.
Springer eBooks, 2003
Collision theory is briefly reviewed in the framework of the wave operator theory of quantum dyna... more Collision theory is briefly reviewed in the framework of the wave operator theory of quantum dynamics which emphasizes the role played by the resonances. Exact expressions of the on-shell S and T matrices are derived for an exactly solvable model which describes several resonances decaying into several channels. This model is especially relevant for investigating the physics near energy thresholds. The formalism is applied to giant resonances and to a model of laser-assisted electron-atom scattering.
Chemical Physics Letters, Aug 1, 1991
Abstract The 11 B quadrupole coupling constants of rovibrational levels of 11 B 1 H in its B 1 ∑ ... more Abstract The 11 B quadrupole coupling constants of rovibrational levels of 11 B 1 H in its B 1 ∑ + state have been computed from molecular wavefunctions which explicitly describe nuclear displacement. The necessary radial rovibrational wavefunctions were obtained by the Fourier-grid-Hamiltonian method. The double-minimum character of the potential is seen to influence profoundly the rovibrational dependence of the boron quadrupole coupling constant. The quadrupole hyperfine patterns are predicted to be markedly different from those corresponding to the previously studied ∑ + states of diatomic molecules represented by single-minimum potentials.
Theoretica chimica acta, May 1, 1994
SummaryWave operator equations associated with the determination of energies are generally solved... more SummaryWave operator equations associated with the determination of energies are generally solved by perturbation methods [1]. However, it is well known that for most actual systems the standard Rayleigh-Schrödinger and Brillouin-Wigner series have slow convergence properties. We suggest that one way how to deal with this problem is to modify or to renormalize the standard wave equations. For that purpose we introduce newderivative andconvergence operators associated with the basic Rayleigh-Schrödinger and Brillouin-Wigner formalisms. Since the direct use of these operators would imply difficult operator inversions, we investigate the efficiency of various approximations of the derivative operator. It is shown that these approximations can overcome convergence difficulties and also open the way to systematic derivations of infinite partial summation schemes. Our approach is also discussed with respect to the standard diagonalization procedure of Davidson. Three simple model systems are investigated numerically.
Chemical Physics, Nov 1, 1991
A modified version of the trajectory surface leaking method for dynamical calculations on autoion... more A modified version of the trajectory surface leaking method for dynamical calculations on autoionizing atom-diatom collision systems is elaborated. The modification is designed so as to account for the most prominent quantum features of the ionization event. Test calculations on He(2 %)-Hz are presented. The approach is found to yield an improved picture of the He(2 'S)-HZ+ [He...H: ] +e-ionization event, which is consistent with Penning electron spectra measurements. Some implications for future theoretical studies of atom-diatom autoionizing collision systems are outlined.
Chemical Physics, Sep 1, 1986
Abstract The possibility of non-adiabatic behaviour of the He(21S)-H2 and He(23S)-H2 collision sy... more Abstract The possibility of non-adiabatic behaviour of the He(21S)-H2 and He(23S)-H2 collision systems is reexamined by means of extended diatomics-in-molecules calculations. In the triplet case, the calculations support the idea that at collision energies above ≈ 1 eV the system could behave non-adiabatically. In the singlet He*-H2 system, a break-down of the Born-Oppenheimer approximation is predicted to take place at higher energies.
The Journal of Chemical Physics, 2015
We propose a simple method for calculation of low-lying shape electronic resonances of polyatomic... more We propose a simple method for calculation of low-lying shape electronic resonances of polyatomic molecules. The method introduces a perturbation potential and requires only routine bound-state type calculations in the real domain of energies. Such a calculation is accessible by most of the free or commercial quantum chemistry software. The presented method is based on the analytical continuation in a coupling constant model, but unlike its previous variants, we experience a very stable and robust behavior for higher-order extrapolation functions. Moreover, the present approach is independent of the correlation treatment used in quantum many-electron computations and therefore we are able to apply Coupled Clusters (CCSD-T) level of the correlation model. We demonstrate these properties on determination of the resonance position and width of the 2Πu temporary negative ion state of diacetylene using CCSD-T level of theory.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2002
Standard Fano profiles can be described in terms of two interacting quasi-bound states. The theor... more Standard Fano profiles can be described in terms of two interacting quasi-bound states. The theory of Fano profiles is extended to line profiles implying several interfering quasi-bound states. New analytical expressions of the lineshapes are derived. The concept of the shape polynomial is introduced which permits one to generalize the parameters of the Fano theory.
International Journal of Quantum Chemistry, 1990
A practical procedure for calculation of nuclear quadrupole coupling constants for light diatomic... more A practical procedure for calculation of nuclear quadrupole coupling constants for light diatomic molecules is discussed. The procedure is based on a molecular wave function that explicitly describes nuclear motion. The approach is capable of yielding quadrupole coupling constants for excited rovibrational levels of diatomic molecules in their ground and excited electronic states. An application of the procedure to the X1Σ+g and B1Σ+u states of HD and D2 is presented.
International Journal of Quantum Chemistry, 1990
The 2H, 6Li, and 7Li quadrupole coupling constants of the low‐lying rovibrational levels in the X... more The 2H, 6Li, and 7Li quadrupole coupling constants of the low‐lying rovibrational levels in the X1∑+ and A1∑+ electronic states of 7Li2H, 6Li2H, 7Li1H, and 6Li1H are calculated from molecular wave functions which explicitly describe nuclear motion. Except for the lithium coupling constants in the A1∑+ state, the vibrational dependence of the nuclear quadrupole coupling is found to be significant for all the studied isotopic species. On the other hand, the rotational dependence appears to be important only for the deuteron coupling constant of 7Li2H and 6Li2H in the A1∑+ state. Special attention is paid to relative magnitudes of the Li and D quadrupole coupling constants in the 7Li2H and 6Li2H isotopic species. The information about the relative magnitudes and their changes with vibrational excitation is used to outline a theoretical approach to the interpretation of the hyperfine structure of the spectra of these species.
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Papers by Ivana Paidarova