Accurate Double Many-Body Expansion Potential Energy Surface for the Lowest Singlet State of Methylene

Abstract

A single-sheeted double many-body expansion potential energy surface is reported for ground-state CH 2 by fitting accurate ab initio energies that have been semiempirically corrected by the double many-body-expansion scaled-external-correlation method. The energies of about 2500 geometries have been calculated using the multireference configuration interaction method, with the single diffusely corrected aug-cc-pVQZ basis set of Dunning and the full valence complete active space wave function as reference. The topographical features of the novel global potential energy surface are examined and compared with other potential energy surfaces.

Dynamical importance of van der Waals saddle and excited potential surface in C(1D)+D2 complex-forming reaction

“…have developed a global ab initio PES (called Bussery-Honvault-Honvault-Launay (BHL)) for the state; later, the ab initio data are refitted with the reproducing kernel Hilbert space (RKHS) method to remove some spurious features of the BHL PES, and the modified PES is denoted as the RKHS PES27. Although there are other PESs and subsequent dynamical calculations2829, the RKHS PES is the most widely used in dynamical studies273031323334. Most recently, a highly accurate global ab initio PES (or Zhang-Ma-Bian-a (ZMB-a)) has been constructed by our group35, which is unique in the accurate description of the regions of vdW interactions and around conical intersections (CIs), and further dynamical calculations36 performed on this PES for the C( 1 D )+H 2 reaction confirm its accuracy.…”

Global analytical ab initio ground-state potential energy surface for the C(1D)+H2 reactive system

“…We suppose that these 2D-vdW wells on the DMBE surface are too deep, though the ab initio values for the 2D-well depths are not reported by Joseph and Varandas. 16 It is clear that the ZMB-a surface gives a better description of the long-range vdW regions, which support three vdW complexes, since these parts of our PES are fitted with great care to match ab initio calculations.…”

“…It is known that the BHL surface 12 has deficiencies in the long range area, whereas the vdW interaction is illustrated graphically on the DMBE surface. 16 The extremal point of the vdW interaction in the entrance channel on the DMBE surface is at a linear C-HH geometry with R CH = 5.5 bohrs, R HH = 1.401 bohrs, the energy of which is around 0.8 kcal/mol lower than the C( 1 D)+H 2 asymptote. The feature of the entrance valley of our surface is in generally good agreement with that of the DMBE surface.…”

“…Joseph and Varandas 16 did not report the linear H-CH barrier height on the DMBE PES, but we estimate it to be visibly lower than our ab initio value of 9.29 kcal/mol, according to the contour plots presented in their paper. 16 Similarly, a contour plot as a function of R CH and R HH in the linear C-H-H configuration space is shown in Fig. 6(a), with the red dots indicating the CI seam.…”

“…Based on the same set of ab initio data, a further refinement of the BHL surface was presented by Bañares et al 15 using the Reproducing Kernel Hilbert Space (RKHS) interpolation method. Recently, Joseph and Varandas 16 constructed a double many-body expansion (DMBE) PES for the 1 1 A state, and this surface a) Electronic mail: mht@iccas.ac.cn b) Electronic mail: bian@iccas.ac.cn gives a good description of the long range area. The surfaces for the 1 1 A state show no barrier in the C( 1 D) atom perpendicularly attacking H 2 molecule approach and a high barrier in the C( 1 D) atom collinearly attacking H 2 molecule direction.…”