CCSD(T) and CR-CCSD(TQ),b results for the potential energy curve of the N2 molecule, as described by the DZ basis set (113), shown in Table 1 and Figure 1. [Pg.55]

These discrepancies result (a) from the harmonic approximation used in all calculations [to,- (theory) > v, (exp)], (b) the known deficiencies of minimal and DZ basis sets to describe three-membered rings [polarization functions are needed to describe small CCC bond angles a>,(DZ + P) > w,(DZ) > to,(minimal basis)] and (c) the need of electron correlated wave functions to correctly describe the curvature of the potential energy surface at a minimum energy point [ [Pg.102]

In the seventies and eighties, ab initio calculations on potentially homoaromatic molecules were preferentially carried out with the Hartree-Fock (HF) method using minimal or double-zeta (DZ) basis sets. However, neither HF nor small basis sets are appropriate to describe a homoaromatic system. In the case of cyclopropyl homoconjugation, the use of a DZ + P basis set is mandatory since polarization (P) functions are needed to describe the bond arrangements of a three-membered ring. [Pg.391]

C. AB4 Molecules.—It is convenient to divide these molecules into tetrahalides AX4, where X=F, Cl, Br, or I, and AY4, where Y=0 or S. In view of the successes of minimal basis set SCF calculations in the prediction of qualitatively correct molecular geometries,3 71-73 we should first refer to an important paper by Ungemach and Schaefer.74 These authors also point out that usually DZ basis sets provide geometry predictions approaching quantitative accuracy, and the addition of polarization functions to the basis set had very little effect on the geometrical predictions. [Pg.9]

Acyloxyl cations R—have been the subject of a detailed study at the MBS level by Maier and Reetz.173 DZ basis sets were also used. The cyclic dioxiryl... [Pg.21]

Recently a more extensive set of calculations using a DZ basis set with full geometry optimization showed the carbene to be ca. 50 kJ mol-1 lower in energy.176 The reaction path for the conversion was also studied, and the authors found E for the ring opening of 30.5 kJ mol-1. [Pg.22]

In a later note,203 they conclude that non-vertical transitions are responsible for the V-N band, and the broad diffuse nature of the spectrum in this region could be caused by two states in close proximity which have the same symmetry as the twisted ethylene. A more extensive series of calculations including Cl and the (9,5)->[4,2] DZ basis set augmented by diffuse functions were carried out by Bender et a/.204... [Pg.25]

An alternative reaction which gives rise to C2H4 is the rearrangement of methylcarbene, MeCH. This reaction can occur in a variety of ways, and Altmann et al.217 carried out SCF calculations with a DZ basis set on two cross-sections of the potential hypersurface. The first cross-section was investigated in an MBS calculation of the variation of E with the CCH angle. [Pg.27]

Sundberg and Cheung283 used a somewhat smaller than DZ basis set and per-... [Pg.36]

MgO, the next oxide in this series, has been the subject of numerous experimental and theoretical studies. An extensive series of calculations at the SCF level for six different configurations was reported by Schamps and Lefebvre-Brion,309 who give references to earlier work. These calculations used an extended DZ basis set and are consequently more accurate than previous work. [Pg.119]

The ground state force field, vibrational normal modes and frequencies have been obtained with MCSCF analytic gradient and hessian calculations [176]. Frequencies computed with the DZ basis set are compared with experimental ones in Table 16. The T - So transition moments were obtained using distorted benzene geometries with atomic displacements along the normal modes, and with the derivatives in Eq. 97 obtained by numerical differentiation. The normal modes active for phosphorescence in benzene are depicted in Fig. 12. The final formula for the radiative lifetime of the k spin sublevel produced by radiation in all (i/f) bands is (ZFS representation x,y,z is used [49]) ... [Pg.135]

Table 5-2. Spectroscopic constants for the N2 molecule obtained with different methods and the DZ basis set... |

See also in sourсe #XX -- [ Pg.443 , Pg.444 ]

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