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001-es BibID:	BIBFORM084881
Első szerző:	Bende, A.
Cím:	Ab initio study of the ammonia-ammonia dimer: BSSE-free structures and intermolecular harmonic vibrational frequencies / A. Bende, Á. Vibók, G. J. Halász, S. Suhai
Dátum:	2004
ISSN:	0020-7608
Megjegyzések:	The influence of basis set superposition error (BSSE) in optimized geometries, force constants and intermolecular harmonic vibrational frequencies of the ammonia?ammonia dimer have been studied both at the Hartree?Fock and correlated (second-order Mller?Plesset perturbation theory) levels of theory using several different basis sets as (6-31G, 6-311G, 6-31 G, 6-311 G, 6-31G(d,p), 6-311G(d,p), 6-31 G(d,p) 6-311 G(d,p) and 6-311 G(2d,2p)). The widely used a posteriori Boys?Bernardi "counterpoise" (CP) correction scheme has been compared with the a priori method utilizing the chemical Hamiltonian approach (CHA). The results show that practically there is no difference between these two methods, so the a priori CHA scheme can be considered as an ultimate solution of the BSSE problem. It is also concluded that the BSSE influence is very significant, so removing this effect is very important.
Tárgyszavak:	Természettudományok Fizikai tudományok idegen nyelvű folyóiratközlemény külföldi lapban folyóiratcikk basis set superposition error chemical Hamiltonian approach harmonic vibrational frequencies intermolecular interactions
Megjelenés:	International Journal Of Quantum Chemistry. - 99 : 5 (2004), p. 585-593. -
További szerzők:	Vibók Ágnes (1962-) (fizikus) Halász Gábor J. (1961-) (fizikus) Suhai Sándor
Pályázati támogatás:	T037934 OTKA
Internet cím:	Szerző által megadott URL DOI Intézményi repozitóriumban (DEA) tárolt változat
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001-es BibID:	BIBFORM085982
Első szerző:	Halász Gábor J. (fizikus)
Cím:	Toward a BSSE-free description of strongly interacting systems / G. J. Halász, Á. Vibók, S. Suhai, I. Mayer
Dátum:	2002
ISSN:	0020-7608
Megjegyzések:	The so-colled "chemical Hamiltonian approach"(CHA) gives perfect a priori BSSE-free description of weak intermolecular interactions, but has been found inappropriate for describing strong interactions taking place with in a molecule. Here, we propose a simple modi?cation of the CHA/F BSSE-free SCF method, which retains all the good properties of the CHA/F method for the intermolecular case but can be used also to describe covalent and ionic interactions.This is vital for calculating whole potential surfaces of chemical reactions in a consistent manner, which was found impossible by using the a posteriori counterpoise correction method. Model calculations are presented for covalent and ionic chemical bonds and for a rare gas?proton system.
Tárgyszavak:	Természettudományok Fizikai tudományok idegen nyelvű folyóiratközlemény külföldi lapban folyóiratcikk basis set superposition error (BSSE) covalent and ionic bonds chemical Hamiltonian approach (CHA) BSSE-free SCF theory
Megjelenés:	International Journal of Quantum Chemistry. - 89 : 4 (2002), p. 190-197. --
További szerzők:	Vibók Ágnes (1962-) (fizikus) Suhai Sándor Mayer István
Pályázati támogatás:	T25369 OTKA T34812 OTKA FKFP 0498/2000 Egyéb
Internet cím:	Szerző által megadott URL DOI Intézményi repozitóriumban (DEA) tárolt változat
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001-es BibID:	BIBFORM084882
Első szerző:	Vibók Ágnes (fizikus)
Cím:	Analytic-numerical approach to calculate electronic nonadiabatic coupling terms: Study of the C2H molecule and the H2 + H system / Á. Vibók, G. Halász, A. M. Mebel, S. Hu, M. Bae
Dátum:	2004
ISSN:	0020-7608
Megjegyzések:	The Curl equations (Baer, M. Chem Phys Lett 1975, 35, 112) are applied to calculate the nonadiabatic coupling terms, ij, subject to ab initio boundary conditions. As an example we consider a two-state, planar system characterized by two (polar) coordinates, and q, and treat the corresponding components of , namely, (q, ) and q(q, ). The main difficulty that we encounter is that the vectorial Curl equation supplies, for this case, only one differential equation although we have two unknown functions. To overcome this difficulty we employ a gauge transformation that leads to a divergence equation?the missing equation. Next, the two Curl?divergence equations are treated with the aim of forming two decoupled second-order differential equations for the two components of a vector potential A(q, ) [which is related to (q, ) through a gauge transformation], namely, one for A (q, ) [related to (q, )] and one for Aq(q, ) [related to q(q, )]. The main achievement of the theory is a relation, for a given q1, between the Fourier coefficients of q(q, ) and those of (q, ). This approach is applied to three cases: an analytic model and two ab initio treatments?one for the C2H molecule and one for the H H2 molecular system. In all three cases encouraging agreements were obtained between the ab initio-calculated values of q(q, ) values and the ones that follow from the present approach.
Tárgyszavak:	Természettudományok Kémiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban folyóiratcikk Curl equations nondiabetic coupling terms conical intersection topological phase
Megjelenés:	International Journal Of Quantum Chemistry. - 99 : 5 (2004), p. 594-604. -
További szerzők:	Halász Gábor J. (1961-) (fizikus) Mebel, Alexander M. Hu, S. Baer, Michael
Internet cím:	Szerző által megadott URL DOI Intézményi repozitóriumban (DEA) tárolt változat
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