Vertical spectrum of ethene: uncontracted versus contracted correlation methods and the role of the adapted molecular orbitals

Pérez-Casany, M. Pilar; Nebot–Gil, Ignacio; Sánchez‐Marín, José; Castell, O.; Malrieu, Jean‐Paul

doi:10.1016/s0009-2614(98)00933-6

Cited by 16 publications

(6 citation statements)

References 28 publications

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“…Other works 10,48,49 have also shown that the use of the orbitals of the T (neutral in nature) or N (with a large neutral component) states or those of the cation give results in better agreement with the best estimates. All these states are expected to have p orbitals more contracted than those of the V state if the dynamic σ polarization is not considered in the orbital optimization.…”

Section: Analysis Of the Nature Of The Ionic Statesmentioning

confidence: 95%

On the nature of the π → π* ionic excited states: The V state of ethene as a prototype

2008

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This article addresses an analysis of the physical effects required for the correct description of the ionic pi --> pi* excited states in the frame of ab initio quantum chemistry, using the ionic V state of the ethene molecule as an example. The importance of the dynamic sigma polarization (absent in methods where the sigma skeleton is treated at a mean-field level) has been recognized by many authors in the past. In this article a new physical effect is described, i.e. the spatial contraction of the pi and pi* molecular orbitals (or of the local p atomic orbitals) originated from the reduction of the ionicity due to the dynamic sigma polarization. Such an effect is a second-order effect (it appears only as a consequence of the dynamic sigma polarization) but it cannot be ignored. Many of the difficulties found in the past in the calculation of the vertical excitation energy of the ionic states are attributed to an incomplete description of this contraction, while the few successes have been obtained when it has been fortuitously introduced by ad hoc procedures or when it is described in a brute force approach. Various strategies are proposed to allow for the spatial contraction of the p atomic orbitals. If this effect is considered at the orbital optimization step, it is shown that for the V state of ethene no Rydberg/valence mixing occurs and a simple perturbation correction (to the second order in the energy) on the pi --> pi* singly excited configuration gives stable results with respect to the computational parameters and in good agreement with the experimental findings and with the best theoretical calculations. Moreover, our results confirm the indication of Müller et al. (J Chem Phys 1999, 110, 7176) that the transition to the V state of ethene conforms to the Franck-Condon principle and that it is not necessary to appeal to a nonvertical transition to interpret the experimental data. The strategy reported in this article for ethene can be in principle generalized to the pi --> pi* ionic excited states of other molecules.

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Section: Analysis Of the Nature Of The Ionic Statesmentioning

confidence: 95%

On the nature of the π → π* ionic excited states: The V state of ethene as a prototype

2008

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“…A five electron system seems then a good choice. Rydberg‐valence mixing is a challenging problem for most approximated methods23–30 and some of the lower Rydberg states of Σ + symmetry in BeH can mix with the first Σ + valence excited state 23. Moreover, the open‐shell character adds some difficulties into approximated methods that can be sensitive to the choice of the set of one‐electron molecular orbital (MO) functions 31–34.…”

Section: Introductionmentioning

confidence: 99%

Full configuration interaction calculation of the low lying valence and Rydberg states of BeH

2007

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The all-electron full configuration interaction (FCI) vertical excitation energies for some low lying valence and Rydberg excited states of BeH are presented in this article. A basis set of valence atomic natural orbitals has been augmented with a series of Rydberg orbitals that have been generated as centered onto the Be atom. The resulting basis set can be described as 4s2p1d/2s1p (Be/H) + 4s4p3d. It allows to calculate Rydberg states up to n= {3,4,5} of the s, p, and d series of Rydberg states. The FCI vertical ionization potential for the same basis set and geometry amounts to 8.298 eV. Other properties such as FCI electric dipole and quadrupole moments and FCI transition dipole and quadrupole moments have also been calculated. The results provide a set of benchmark values for energies, wave functions, properties, and transition properties for the five electron BeH molecule. Most of the states have large multiconfigurational character in spite of their essentially single excited nature and a number of them present an important Rydberg-valence mixing that is achieved through the mixed nature of the particle MO of the single excitations.

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“…Despite the small dimension of the molecule and the relative simplicity of the qualitative description of this state, it has been the subject a large series of theoretical studies in the last decades (see Refs. 4–18 for some recent articles). This is due to the fact that the most sophisticated theoretical methods found an unusual difficulty in describing consistently this state, that is, to be in agreement among themselves and with the experimental findings.…”

Section: Introductionmentioning

confidence: 99%

Polymer nanofibers prepared by template melt extrusion

2005

J of Applied Polymer Sci

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ABSTRACT:Combining the template method with the extrusion technology, polymer nanofibers have been prepared when molten polymer is forced through the pores of anodic aluminum membrane and cooled to complete the nanofiber formation process. The microstructures of nanofibers are determined by SEM, TEM, XRD, and DSC. The results suggest that the PE nanofibers consist of extendedchain crystals and the transition from an orthorhombic to a hexagonal phase and the latter phase melting occurs at 159.8°C.

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Vertical spectrum of ethene: uncontracted versus contracted correlation methods and the role of the adapted molecular orbitals

Cited by 16 publications

References 28 publications

On the nature of the π → π* ionic excited states: The V state of ethene as a prototype

On the nature of the π → π* ionic excited states: The V state of ethene as a prototype

Full configuration interaction calculation of the low lying valence and Rydberg states of BeH

Polymer nanofibers prepared by template melt extrusion

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