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- Muammar El Khatib, Oriana Brea, Edoardo Fertitta, Gian Luigi Bendazzoli, Stefano Evangelisti, Thierry Leininger
- The Journal of chemical physics
- 2015

The Total Position Spread (TPS) tensor, defined as the second moment cumulant of the position operator, is a key quantity to describe the mobility of electrons in a molecule or an extended system. In the present investigation, the partition of the TPS tensor according to spin variables is derived and discussed. It is shown that, while the spin-summed TPS… (More)

- Muammar El Khatib, Gian Luigi Bendazzoli, +4 authors Celestino Angeli
- The journal of physical chemistry. A
- 2014

The bond nature in beryllium dimer has been theoretically investigated using high-level ab initio methods. A series of ANO basis sets of increasing quality, going from sp to spdf ghi contractions, has been employed, combined with HF, CAS-SCF, CISD, and MRCI calculations with several different active spaces. The quality of these calculations has been checked… (More)

- Gian Luigi Bendazzoli, Muammar El Khatib, Stefano Evangelisti, Thierry Leininger
- Journal of Computational Chemistry
- 2014

The behavior of the Total Position Spread (TPS) tensor, which is the second moment cumulant of the total position operator, is investigated in the case of a mixed-valence model system. The system consists of two H2 molecules placed at a distance D. If D is larger than about 4 bohr, the singly ionized system shows a mixed-valence character. It is shown that… (More)

- Oriana Brea, Muammar El Khatib, Celestino Angeli, Gian Luigi Bendazzoli, Stefano Evangelisti, Thierry Leininger
- Journal of chemical theory and computation
- 2013

The behavior of the Position-Spread Tensor (Λ) in a series of light diatomic molecules (either neutral or negative ions) is investigated at a Full Configuration Interaction level. This tensor, which is the second moment cumulant of the total position operator, is invariant with respect to molecular translations, while its trace is also rotationally… (More)

- Laura Gagliardi, Gian Luigi Bendazzoli, Stefano Evangelisti
- Journal of Computational Chemistry
- 1997

We present a method for the direct generation of the lists of Ž . strings, suited for integral-driven full-CI FCI algorithms. This method generates the string lists each time they are used, and hence sensibly reduces the memory requirements, compared to our previous method that precalculates the lists. It was also extended to permit a truncation of the… (More)

- Celestino Angeli, Gian Luigi Bendazzoli, Stefano Evangelisti
- The Journal of chemical physics
- 2013

A closed analytical formula for the localization tensor of the Heitler-London and related wavefunctions of the hydrogen molecule is given. For the wavefunctions with a well defined nature, the various contributions of the analytical expressions can be interpreted in simple terms. The results are then compared with full configuration interaction… (More)

- Edoardo Fertitta, Muammar El Khatib, Gian Luigi Bendazzoli, Beate Paulus, Stefano Evangelisti, Thierry Leininger
- The Journal of chemical physics
- 2015

The spin partition of the Total Position-Spread (TPS) tensor has been performed for one-dimensional Heisenberg chains with open boundary conditions. Both the cases of a ferromagnetic (high-spin) and an anti-ferromagnetic (low-spin) ground-state have been considered. In the case of a low-spin ground-state, the use of alternating magnetic couplings allowed to… (More)

- Antonio Monari, Jose Pitarch-Ruiz, Gian Luigi Bendazzoli, Stefano Evangelisti, Jose Sanchez-Marin
- Journal of chemical theory and computation
- 2008

The Li4 cluster low lying electronic states were studied. In particular we investigated the tetrahedral geometry at full CI and coupled cluster level, with basis sets of increasing quality. The (5)A2 electronic state, characterized by having all the valence electrons unpaired, forming a quite stable no-pair bonding state, was studied in greater detail. In… (More)

- Muammar El Khatib, Stefano Evangelisti, Thierry Leininger, Gian Luigi Bendazzoli
- Physical chemistry chemical physics : PCCP
- 2012

The electronic structure of planar molecular edifices obtained by joining polyacene fragments (polyacene stripes) is investigated at tight-binding and ab initio levels. It is shown that the presence of 60° angles in the molecular skeleton induces the formation of singly-occupied molecular orbitals, whose combination gives rise to quasi-degenerate electronic… (More)

- Elda Rossi, Gian Luigi Bendazzoli, Stefano Evangelisti
- Journal of Computational Chemistry
- 1998