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Multireference configuration interaction calculations for the reaction: A correlation scaled ground state potential energy surface
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Image of FIG. 1.
FIG. 1.

extrapolation for and energies to the CBS limit, indicating clear convergence (see inset) in the exothermicity as a function of . The small residual error in (dashed line) due to active space size in the calculations is corrected by correlation scaling (see text for details).

Image of FIG. 2.
FIG. 2.

Correlation energy recovered for each basis set, . The nearly constant ratio of recovered correlation energy relative to CBS extrapolation (see inset) illustrates how correlation scaling effectively mimics a larger active space.

Image of FIG. 3.
FIG. 3.

F–H–Cl transition state geometry at various levels of theory, all confirming a sharply bent transition state: (a) /aug-cc-pVTZ; (b) /CBS/scaled; RCCSD(T)/aug-cc-pVTZ.

Image of FIG. 4.
FIG. 4.

The DW-MCSCF energies (a) and weights (b) as a function of reaction coordinate, with up to six states dynamically weighted. Note the strongly avoided crossings of and charge transfer (CT) states with surfaces correlating to the ground state asymptotes. Note also the smooth weight adjustment from a three-state calculation at either asymptote to states near the transition state geometry.

Image of FIG. 5.
FIG. 5.

reaction path at the MCSCF, , and correlation scaled levels, indicating relatively minor effects due to correlation scaling.

Image of FIG. 6.
FIG. 6.

2D slice of the fitted surface with global rms of .

Image of FIG. 7.
FIG. 7.

Ground reference state coefficient in the /aug-cc-pVQZ wave function, indicating strong admixture of excited state character near the transition state geometries closest to the conical intersection (marked by asterisks).

Image of FIG. 8.
FIG. 8.

PES vs contours for (a) transition state and (b) collinear bend angles. Conical intersection seams occur to each side of the transition state; the seam location closest to the reaction path is marked by the asterisk. Contour spacing is with respect to .

Image of FIG. 9.
FIG. 9.

F–H–Cl bending potential corresponding to transition state (dashed) and conical intersection seam (solid) and bond lengths, with eigenvalues obtained from a rigid bender analysis. Note that the conical intersection is lower than the transition state with only a barrier to linearity from the reaction path.

Image of FIG. 10.
FIG. 10.

(a) 2D effective transition state barrier height (solid) and HCl bond length (dashed) as a function of F–H–Cl bending angle (dotted line is for HCl). As decreases below , both the HCl bond length and barrier height increase dramatically from transition state values, characteristic of a shift from an “early” to “late” transition state. (b) Trajectory analysis for F–HCl angular deflection as a function of initial bend angle, . For low , only a very narrow range (dark gray) of incident scattering angles are successfully “prerotated” (light gray) into the appropriately bent transition state angle to react.


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Table I.

Exothermicity in kcal/mol of calculated by various ab initio methods. Calculated energies are corrected for zero-point (Refs. 72–75) and spin-orbit (Ref. 76) which are not included in the single surface ab initio calculations. The experimental is (Refs. 65 and 66).

Generic image for table
Table II.

Diatomic constants from ab initio PES calculated at compared with the correlation scaled values and experiment (Refs. 72–75, 88, and 89).

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Table III.

The geometries and energies of the transition state for a range of methods and basis sets. In particular, the transition state geometry is strongly bent at all levels of theory.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Multireference configuration interaction calculations for the F(P2)+HCl→HF+Cl(P2) reaction: A correlation scaled ground state (1A′2) potential energy surface