
HAJGATO, Balazs; DELEUZE, Michael
Nonlocal MP2like electron correlation in DFT calculations employing the double hybrid dispersion corrected B2PLYD functional is found to systematically quench antiferromagnetism in a variety of hexagonal graphene nanoflakes. The scaling in size of the associated spin contamination demonstrates further the artefactual character of any spinpolarization of electron densities in singlet electronic states.

HUZAK, Matija; HAJGATO, Balazs; DELEUZE, Michael
The vertical and adiabatic singlettriplet energy gaps, electron affinities and ionization energies of azulene, phenanthrene, pyrene, chrysene, and perylene are computed by applying the principles of a focal point analysis onto a series of singlepoint calculations at the level of HartreeFock theory, second, third, and fourthorder MollerPlesset perturbation theory, as well as coupled cluster theory including single, double and perturbative triple excitations, in conjunction with correlation consistent basis sets of improving quality. Results are supplemented with an extrapolation to the limit of an asymptotically complete basis set. According to our best estimates, azulene, phenanthrene, pyrene, chrysene, and perylene exhibit adiabatic...

Hajgato, Balazs; Morini, Filippo; Deleuze, Michael
The main purpose of this work is to reinvestigate the influence of nuclear dynamics in the electronic ground state of group 6 metal hexacarbonyl compounds [W(CO)6, Cr(CO)6, Mo(CO)6] on electron momentum density profiles obtained from experimental orbital reconstructions employing Electron Momentum Spectroscopy. We call into questionthe view (Liu et al. in Chem Phys Lett 497:229, 2010) that thermally induced nuclear displacements associated with the first three triply degenerate 1T2g, 1T1u, and 1T2u vibrational eigenmodes can be large enough at or near room temperature (298–310K) to explain on their own the unexpectedly large electron densities inferred for the frontier orbitals of...

Knippenberg, Stefan; HAJGATO, Balazs
In line with a recent study of the electronic structure of the cage compound norbornane (J. Chem. Phys. 121 (2004), 10525:J. Phys. Chem. A 109 (2005), 4267), symmetry adapted cluster expansion configuration interaction (SACCI) general R calculations have been performed and compared with results obtained by the third order algebraic diagrammatic construction scheme [ADC(3)]. Comparison has been made with previously performed electron momentum spectroscopy (EMS) and ultraviolet photoelectron measurements. The region around similar to 25eV (band 12), characterized by an elaborated band in the EMS spectrum which is missing in previous Green's function and ADC calculations, is investigated. This study...

Hajgato, Balazs; Huzak, Matija; Deleuze, Michael S.
A benchmark theoretical study of the electronic ground state and of the vertical and adiabatic singlettriplet (ST) excitation energies of nacenes (C4n+2H2n+4) ranging from octacene (n = 8) to undecacene (n = 11) is presented. The T1 diagnostics of coupled cluster theory and further energybased criteria demonstrate that all investigated systems exhibit predominantly a 1Ag singlet closedshell electronic ground state. Singlettriplet (S0T1) energy gaps can therefore be very accurately determined by applying the principle of a focal point analysis (FPA) onto the results of a series of singlepoint and symmetryrestricted calculations employing correlation consistent ccpVXZ basis sets (X = D,...

Huzak, Matija; Deleuze, Michael S.; Hajgato, Balazs
An analysis using the formalism of crystalline orbitals for extended systems with periodicity in one dimension demonstrates that any antiferromagnetic and halfmetallic spinpolarization of the edge states in nacenes, and more generally in zigzag graphene anoislands and nanoribbons of finite width, would imply a spin contamination that increases proportionally to system size, in sharp and clear contradiction with the implications of Lieb’s theorem for compensated bipartite lattices and the expected value for a singlet (S = 0) electronic ground state. Verifications on naphthalene, larger nacenes (n = 3–10) and rectangular nanographene islands of increasing size, as well as a...

Shojaei, S.H.Reza; Morini, Filippo; Hajgato, Balazs; Deleuze, M. S.
The results of experimental studies of the valence electronic structure of 1butene employing photoelectron spectroscopy as well as electron momentum spectroscopy are interpreted on the ground of quantitative calculations of oneelectron and shakeup ionization energies and of the related Dyson orbitals, using oneparticle Green's function theory in conjunction with the thirdorder algebraic diagrammatic construction scheme (ADC(3)). Comparison is made with simulations of (e, 2e) electron momentum distributions obtained from standard (B3LYP) KohnSham orbitals. Our analysis is based on highly quantitative determinations of the energy difference between the cis and gauche (C(1)) conformers, within similar to 0.02 kcal mol(1) accuracy, and...

Shojaei, S.H.Reza; Morini, Filippo; Hajgato, Balazs; Deleuze, Michael S.
The results of experimental studies of the valence electronic structure of 1butene employing
photoelectron spectroscopy as well as electron momentum spectroscopy are interpreted on the
ground of quantitative calculations of oneelectron and shakeup ionization energies and of the
related Dyson orbitals, using oneparticle Green’s function theory in conjunction with the
thirdorder algebraic diagrammatic construction scheme (ADC(3)). Comparison is made with
simulations of (e, 2e) electron momentum distributions obtained from standard (B3LYP)
Kohn–Sham orbitals. Our analysis is based on highly quantitative determinations of the energy
difference between the cis and gauche (C1) conformers, within ∼0.02 kcal mol−1 accuracy,
and a thermostatistical evaluation thereby of conformer weights beyond the level...

Shojaei, S.H.Reza; Hajgato, Balazs; Deleuze, Michael S.
An extensive study of the valence electronic structure, ionization spectrum and electron momentum distributions
of pyrimidine is presented, on the ground of accurate calculations of oneelectron and shakeup
ionization energies and of the related Dyson orbitals, using oneparticle Green’s Function theory in
conjunction with the thirdorder Algebraic Diagrammatic Construction scheme [ADC(3)]. Comparison
is made with results obtained from standard (B3LYP) Kohn–Sham orbitals and recent measurements
employing Electron Momentum Spectroscopy. Quantitative insights into the experimental momentum
distributions are amenable without resorting to any empirical rescaling of pole strengths, provided band
overlaps and relaxation effects are properly accounted for.

Shojaei, S.H.Reza; Morini, Filippo; Hajgató, Bálazs; Deleuze, Michael S.
The results of experimental studies of the valence electronic structure of 1butene employing photoelectron spectroscopy as well as electron momentum spectroscopy are interpreted on the ground of quantitative calculations of oneelectron and shakeup ionization energies and of the related Dyson orbitals, using oneparticle Green's function theory in conjunction with the thirdorder algebraic diagrammatic construction scheme (ADC(3)). Comparison is made with simulations of (e, 2e) electron momentum distributions obtained from standard (B3LYP) Kohn–Sham orbitals. Our analysis is based on highly quantitative determinations of the energy difference between the cis and gauche (C1) conformers, within ~0.02 kcal mol−1 accuracy, and a thermostatistical...

Monten, Ruben; HAJGATO, Balazs; DELEUZE, Michael
The static dipole polarizabilities of Ne, CO, N(2), F(2), HF, H(2)O, HCN, and C(2)H(2) (acetylene) have been determined close to the FullCI limit along with an asymptotically complete basis set (CBS), according to the principles of a Focal Point Analysis. For this purpose the results of Finite Field calculations up to the level of Coupled Cluster theory including Single, Double, Triple, Quadruple and perturbative Pentuple excitations [CCSDTQ(P)] were used, in conjunction with suited extrapolations of energies obtained using augmented and doublyaugmented Dunning's correlation consistent polarized valence basis sets of improving quality. The polarizability characteristics of C(2)H(4) (ethylene) and C(2)H(6) (ethane)...

HUZAK, Matija; DELEUZE, Michael; HAJGATO, Balazs
An analysis using the formalism of crystalline orbitals for extended systems with periodicity in one dimension demonstrates that any antiferromagnetic and halfmetallic spinpolarization of the edge states in nacenes, and more generally in zigzag graphene nanoislands and nanoribbons of finite width, would imply a spin contamination < S(2)> that increases proportionally to system size, in sharp and clear contradiction with the implications of Lieb's theorem for compensated bipartite lattices and the expected value for a singlet (S = 0) electronic ground state. Verifications on naphthalene, larger nacenes (n = 310) and rectangular nanographene islands of increasing size, as well as...

HAJGATO, Balazs; HUZAK, Matija; DELEUZE, Michael
A benchmark theoretical study of the electronic ground state and of the vertical and adiabatic singlet triplet (ST) excitation energies of nacenes (C(4n+2)H(2n+4)) ranging from octacene (n = 8) to undecacene (n = 11) is presented. The T1 diagnostics of coupled cluster theory and further energybased criteria demonstrate that all investigated systems exhibit predominantly a (1)A(g) singlet closedshell electronic ground state. Singlettriplet (S(0)T(1)) energy gaps can therefore be very accurately determined by applying the principle of a focal point analysis (FPA) onto the results of a series of singlepoint and symmetryrestricted calculations employing correlation consistent ccpVXZ basis sets (X =...

HOOYBERGHS, Jef; Indekeu, J. O.
Nonequilibrium wetting transitions are observed in Monte Carlo simulations of a kinetic spin system in the absence of a detailed balance condition with respect to an energy functional. A nonthermal model is proposed starting from a twodimensional Ising spin lattice at zero temperature with two boundaries subject to opposing surface fields. Local spin excitations are only allowed by absorbing an energy quantum (photon) below a cutoff energy E (c) . Local spin relaxation takes place by emitting a photon which leaves the lattice. Using Monte Carlo simulation nonequilibrium critical wetting transitions are observed as well as nonequilibrium firstorder wetting phenomena,...

HAJGATO, Balazs; De Proft, Frank; Szieberth, Denes; Tozer, David J.; DELEUZE, Michael; Geerlingsa, Paul; Nyulaszi, Laszlo
We have used a potential wall method to investigate the role of d orbitals in the a(2) singlyoccupied molecular orbitals of (2)A(2) negative ion states of two molecular series: pyridine, phosphabenzene, arsabenzene, stibabenzene (C5H5X, X = {N, P, As, Sb}), and furan, thiophene, selenophene, tellurophene (C4H4X, X = {O, S, Se, Te}). Unlike for the lower lying doubly occupied orbitals, heteroatom dcarbon p inphase (bonding) interactions in these a(2) orbitals are clearly identified and explain the 0.5 eV stabilization of the (2)A(2) radical anion state in those compounds where the heteroatoms have d orbitals in the valence shell, compared to...

DELEUZE, Michael; HAJGATO, Balazs; MORINI, Filippo; KNIPPENBERG, Stefan
Orbital imaging experiments employing Electron Momentum Spectroscopy are subject to many complications, such as distorted wave effects, conformational mobility in the electronic ground state, ultrafast nuclear dynamics in the final state, or a dispersion of the ionization intensity over electronically excited (shakeup) configurations of the cation. The purpose of the present contribution is to illustrate how a proper treatment of these complications enables us to probe in momentum space the consequences of electron correlation and nuclear dynamics in neutral and cationic states.

Krebsz, Melinda; HAJGATO, Balazs; Bazso, Gabor; Tarczay, Gyoergy; Pasinszki, Tibor
The unstable acetonitrile Nsulfide molecule CH3CNS has been photolytically generated in inert solid argon matrix from 3,4dimethyl1,2,5thiadiazole by 254nm UV irradiation, and studied by ultraviolet spectroscopy and midinfrared spectroscopy. The molecule is stable in the matrix to 254nm UV irradiation, but decomposes to CH3CN and a sulfur atom when broadband UV irradiation is used. Chemiluminescence due to S2 formation from triplet sulfur atoms was detected on warming the matrix to similar to 2025 K. The groundstate structure and potential uni and bimolecular reactions of CH3CNS are investigated using B3LYP, CCSD(T), and MRAQCC quantumchemical methods. CH3CNS is demonstrated to be stable...

SHOJAEIKOHNEHSHAHRI, Reza; HAJGATO, Balazs; DELEUZE, Michael
An extensive study of the valence electronic structure, ionization spectrum and electron momentum distributions of pyrimidine is presented, on the ground of accurate calculations of oneelectron and shakeup ionization energies and of the related Dyson orbitals, using oneparticle Green's Function theory in conjunction with the thirdorder Algebraic Diagrammatic Construction scheme [ADC( 3)]. Comparison is made with results obtained from standard (B3LYP) KohnSham orbitals and recent measurements employing Electron Momentum Spectroscopy. Quantitative insights into the experimental momentum distributions are amenable without resorting to any empirical rescaling of pole strengths, provided band overlaps and relaxation effects are properly accounted for. (C) 2010...

MORINI, Filippo; HAJGATO, Balazs; DELEUZE, Michael
An extensive study, throughout the valence region, of the electronic structure, ionization spectrum, and electron momentum distributions of norbornadiene is presented, on the ground of accurate calculations of valence oneelectron and shakeup ionization energies and of the related Dyson orbitals, using oneparticle Green's function (1pGF) theory in conjunction with the socalled thirdorder algebraic diagrammatic construction scheme [ADC(3)]. Comparison is made with results obtained from standard (B3LYP) KohnSham orbitals and measurements employing electron momentum spectroscopy, taking into account the contamination of inner and outervalence spectral bands by numerous shakeup states. Four relatively intense shakeup lines at 12.1, 16.4, 17.6, and 17.8...

DELEUZE, Michael; KNIPPENBERG, Stefan
A review of an extensive series of theoretical studies of the valence oneelectron and shakeup ionization spectra of polycyclic aromatic hydrocarbons is presented, along with new results for three planar quinone derivatives, obtained using oneparticle Green's function (1pGF) theory along with the socalled thirdorder algebraic diagrammatic construction [ADC(3)] scheme and the outervalence Green's function (OVGF) approximation. These results confirm both for the pi and sigmaband systems the rapid spreading, upon increasing system size, of many shakeup lines with significant intensities at outervalence energies. Linear regressions demonstrate that with large conjugated molecules the location of the shakeup onset in the piband...