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Second-order saddle point

Orbital-based methods can be used to compute transition structures. When a negative frequency is computed, it indicates that the geometry of the molecule corresponds to a maximum of potential energy with respect to the positions of the nuclei. The transition state of a reaction is characterized by having one negative frequency. Structures with two negative frequencies are called second-order saddle points. These structures have little relevance to chemistry since it is extremely unlikely that the molecule will be found with that structure. [Pg.94]

Or, more precisely, a firsl-order saddle paint, where the order indicates the number of dimensions in which the saddle point is a maximum. A second-order saddle point would be a maximum in two dimensions and a minimum in all others. Transition structures are first-order saddle points. [Pg.40]

G and Huzinaga basis sets used for K, Rb and Cs, 6-31+G and 6-31+G on C used for C3H5. 6-31+G. Number of imaginary frequencies is given in parentheses (1) a transition state (2) a second-order saddle point. [Pg.745]

An equivalent linear structure of CoP-CO was found to be a second-order saddle point (N-x = 2) when the 6-31G(d) basis set... [Pg.280]

The MEP for inversion corresponds to 6 = 0 and is characterized by the barrier height VWhen C/2V, > 1, apart from this MEP, there is a path that includes two segments described by Eq. (8.42) and a second-order saddle point. The barrier along this path is greater than V, and equal to U,(l + 2V0/C). The transverse frequency along the straight-line MEP for inversion has a minimum at the saddle point q = 0, 0 = 0 consequently, the vibrationally adiabatic barrier is lower than the static one. [Pg.297]

What kind(s) of stationary points do you think a second-order saddle point connects ... [Pg.42]

We recently investigated the potential energy surface for dissociation of 3 at the CAS(12,12) level [19]. The dissociation process was found to proceed via a transition state of C2V symmetry (5TS). Earlier studies had proposed a D2h transition state [24, 29], however, it was shown that the D2h structure is a second order saddle point rather than a transition state. Single point calculations at... [Pg.424]

Min, global energy minimum Min, energy minimum TS, transition state SP 2, second-order saddle point... [Pg.227]

Fig. 3. Methane inversion at QCISD(T)/6-311+0(3df,2p)//CISD/6-311G, rel. energies in kcal mol" number of imaginary frequencies (NIMAG) in parentheses NIMAG = 0 (minimum), 1 (transition state), 2 (second order saddle point)... Fig. 3. Methane inversion at QCISD(T)/6-311+0(3df,2p)//CISD/6-311G, rel. energies in kcal mol" number of imaginary frequencies (NIMAG) in parentheses NIMAG = 0 (minimum), 1 (transition state), 2 (second order saddle point)...
Quantum chemical calculations of the Ne potential-energy hypersurface have shown that the qualitative shape shongly depends on the choice of the theoretical method and basis set. All the geometries represented in Scheme 6 have been shown to be minima on the potential smface, but most of them do not possess minima at all the levels of theories applied. Hexaazabenzene (13), for example, has a minimum for a stmctme at the HF level of theory. However, this geometry is a second-order saddle point with the density functional theory (DFT) and also at the MP2 level of theory. D2 hexaazabenzene has a minimum structure at DFT, but at the CCSD(T)/aug-cc-pVDZ level, the D2 geometry resembles a van der Waals complex of two N3 units, whereas it is a minimum structure at the CCSD(T)/cc-pVTZ level of theory. Similar behavior has been observed for most of the other isomers. [Pg.3028]

Smith ct al. also reinvestigated the question of the trifurcated structure and found it to be a second-order saddle point, nearly 2 kcal/mol higher in energy than the minimum. [Pg.218]

Figure 29.2 Illustration of stepwise and concerted double proton transfer in naphthazarin, showing the equilibrium configurations (MIN), the (unstable) intermediates (INT), the second-order saddle point (SP2), and the location of the first-order saddle points (SPl). Figure 29.2 Illustration of stepwise and concerted double proton transfer in naphthazarin, showing the equilibrium configurations (MIN), the (unstable) intermediates (INT), the second-order saddle point (SP2), and the location of the first-order saddle points (SPl).

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See also in sourсe #XX -- [ Pg.39 ]

See also in sourсe #XX -- [ Pg.50 ]

See also in sourсe #XX -- [ Pg.51 ]




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