Energy switching approach to potential surfaces: An accurate single-valued function for the water molecule

Abstract

A novel scheme is suggested to construct a global potential energy surface by switching between representations which are optimal for different energy regimes. The idea is illustrated for the electronic ground state of water for which we use as switched functions the many-body expansion potential of Murrell and Carter [J. Chem. Phys. 88, 4887 (1984)] and the polynomial form of Polyansky, Jensen, and Tennyson, [J. Chem. Phys. 101, 7651 (1994)]. By also modifying the former to reproduce the Coulombic behavior at the collapsed molecular limits for vanishingly small interatomic distances and approximately account for the long range forces, the new potential energy surface has been given double many-body expansion quality. The result is a global H2O potential energy surface which has spectroscopic accuracy and may be used for studies of reaction dynamics.

Is there a barrier for the C2v insertion reaction in O(1D)+H2? A test dynamics study based on two-valued energy-switching potential energy surfaces

“…For C Iv geometries, the discrepancy is larger but should have little relevance for low energy dynamics especially if a barrier is involved. Table 2 provides a summary of the QCT calculations carried out in the present work using the ES-2v II and ES-2v III potential energy surfaces [12] for H 2 O described in Section 2 (the calculations for ES-2v I unreasonably underestimate the rate constant at 300 K, probably due to the presence of a barrier above the dissociation limit for C 2v geometries, and hence are not given for brevity). Batches of 500 trajectories have been calculated for each of the six translational energies over the range 0X1 T E tr akcal mol À1 T 12.…”

“…In fact, most O 1 D H 2 dynamics calculations carried out to date have been done under such an assumption, including our own [2] which have been based on the single-valued ES potential energy surface (ES-SV) of [12]. Moreover, the good agreement between the dierential cross-sections obtained from the quasiclassical trajectory (QCT) calculations and the experimentally determined state-resolved ones at low collision energies, E tr T 10 kJ mol À1 , bears witness that the title reaction is consistent with an adiabatic mechanism over a single potential energy surface.…”

“…Although the expectations were that such a barrier plays no signi®cant role on the reactivity under thermal and near thermal conditions, a test analysis of this issue has not yet been carried out. Of course, in the absence of an activation barrier, one expects that 1 A two-valued potential energy surface which aims to reach such a level of reliability has recently been proposed by one of the authors [11] using the energy switching [12] (ES) method. It turns out that some recalibration of its parameters has been found [13] to be necessary as it will be further elaborated below.…”

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“…On the other hand those PES do not dissociate correctly and are not suitable for dynamical studies. In order to correct this behaviour, Varandas used an energy switching approach, joining the spectroscopic description of the bottom well with a semiempirical description of the van der Waals interactions between reactants or products, to build a global single-valued PES for the ground state water molecule [39], ES PES. This approach has been complemented with double and triple-valued potential energy surfaces (ES-2v and ES-3v PESs) for this system [41,42].…”

“…Numerous theoretical studies of its dynamics have also been carried out, for example see [11,13,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], using several potential energy surfaces (PESs) published for this system [29,[32][33][34][35][36][37][38][39][40][41][42][43]. These works have been the subject of partial reviews by Liu [44], Althorpe and Clary [45], Balucani et al [46] and Aoiz et al [47].…”