Second-Order ab Initio Møller−Plesset Study of Optimum Chain Length for Total (Electronic Plus Vibrational) β(−ωσ;ω1,ω2) of a Prototype Push-Pull Polyene

2001 ◽  
Vol 105 (42) ◽  
pp. 9748-9755 ◽  
Author(s):  
Denis Jacquemin ◽  
Benoît Champagne ◽  
Eric A. Perpète ◽  
Josep M. Luis ◽  
Bernard Kirtman
Keyword(s):  
Ab Initio ◽  
Chain Length ◽  
Second Order ◽  
Moller Plesset

Ab initio second-order Møller-Plesset calculation of the vibrational spectra of C4 clusters

1987 ◽  
Vol 141 (5) ◽  
pp. 376-379 ◽  
Author(s):  
D. Michalska ◽  
H. Chojnacki ◽  
B.Andes Hess ◽  
L.J. Schaad
Keyword(s):  
Ab Initio ◽  
Vibrational Spectra ◽  
Second Order ◽  
Moller Plesset

On the accuracy of density functional theory for ion–molecule clusters. A case study of PLn+ clusters of the first and second row hydrides

1996 ◽  
Vol 74 (6) ◽  
pp. 1032-1048 ◽  
Author(s):  
Xabier Lopez ◽  
Jesus M. Ugalde ◽  
Cecilia Sarasola ◽  
Fernando P. Cossio
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Density Functional ◽  
Second Order ◽  
Bond Critical Point ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Dissociation Energies ◽  
Gradient Corrections ◽  
Moller Plesset

PLn+ clusters (n = 1, 2 and L = NH3, OH2, FH, PH3, SH2, CIH) in both their triplet and singlet states have been characterized by common approximate density functional methods, SVWN, BVWN, BLYP, and B3LYP. The phosphorus–ligand distances (R), dissociation energies (D0), triplet–singlet gaps (Δt−s), and several bond properties, such as the electron density (ρ(rc)), the Laplacian [Formula: see text] and the local energy density H(rc) at the bond critical point, were compared with those obtained by accurate ab initio molecular orbital theory, namely, second-order Møller–Plesset (MP2) and G2 theory. In general, it is observed that the local spin density approximation (SVWN) yields stronger bonds than ab initio molecular orbital theory. However, addition of gradient corrections to the exchange functional (BVWN) yields ion–molecule bonds that are too weak. Finally, taking account also of gradient corrections to the correlation functional (BLYP) leads to very close agreement with ab initio results. Among these functional, Becke's hybrid functional, B3LYP, best fit the second-order Møller–Plesset and G2 data, reproducing the qualitative trends observed for the above-mentioned properties of phosphorus clusters, except for [Formula: see text] This fit is particularly good for distances, dissociation energies, and electron densities at the bond critical point, and both methods show similar deviations of the values of binding energies and triplet–singlet gap with respect to the G2 data. Compared with our most accurate ab initio molecular orbital data, namely G2, significant overbinding for the singlets, larger for one-ligand than for two-ligand complexes, and significant overestimation of the triplet–singlet gap for one-ligand complexes is observed for both methods, namely, B3LYP and MP2. The deviations at the second-order Møller–Plesset level of theory are mainly due to the lack of quadratic configuration interaction (QCI) corrections, and this deficiency is also present to some extent in B3LYP. However, for larger clusters these corrections are smaller, therefore the B3LYP functional is expected to lead to accurate descriptions. Key words: DFT, Bader analysis, G2, ion–molecule complexes, phosphorus.

scholarly journals AB INITIO STUDY OF AMMONIA CLUSTERS: (NH3)n (n = 2-6)

2010 ◽  
Vol 8 (3) ◽  
pp. 392-396 ◽  
Author(s):  
Herudi Kandau ◽  
Hanggara Sudrajat ◽  
Andreas Napitupulu ◽  
Syahrul Khairi ◽  
Zaky Al-Fatony ◽  
...  
Keyword(s):  
Perturbation Theory ◽  
Ab Initio ◽  
Ab Initio Calculation ◽  
Dipole Moments ◽  
Second Order ◽  
Basis Sets ◽  
Hartree Fock ◽  
Moller Plesset ◽  
Ammonia Clusters ◽  
Hydrogen Bonded

Hydrogen bonded neutral clusters of ammonia, (NH3)n (n = 2-6), have been theoretically investigated employing the D95++(d,p) (and wherever necessary, higher) basis sets at the Hartree-Fock (HF) level as well as with second-order Møller-Plesset (MP2) perturbation theory. While the ammonia trimer and tetramer exhibit perfect molecular symmetries and are nonpolar, the pentamer and hexamer both optimize with slight deviations from perfect symmetries and are seen to posses marginal, but nonzero dipole moments. The (NH3)n linear clusters are seen to be chemically softer than the corresponding cyclic ones.   Keywords: ab initio calculation, ammonia clusters, Hartree-Fock, Møller-Plesset

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