Nonadiabatic Transition State Theory and Trajectory Surface Hopping Dynamics: Intersystem Crossing Between ³B₁ and ¹A₁ States of SiH₂

Abstract

The ability of time-independent nonadiabatic transition state theory (NA-TST) to reproduce intersystem crossing dynamics obtained from the more computationally demanding Tully fewest switches trajectory surface hopping method is investigated. The two approaches are applied to the intersystem crossing between the ground (1)A1 state and lowest energy (3)B1 state of SiH2, coupled through the spin-orbit interaction. For NA-TST, the transition probabilities are calculated using the Landau-Zener formula and the Delos formula which accounts for tunneling. The fewest switches method produces rate constants of 7.6 × 10(11) s(-1) for the triplet to singlet transition and 5.2 × 10(11) s(-1) for the singlet to triplet transition, using a first-order kinetics model. This corresponds to a triplet electronic state lifetime of 781 fs. The NA-TST predicted rate constants are 1-2 orders of magnitude smaller, leading to a larger triplet state lifetime, as compared with the fewest switches method. This discrepancy cannot be explained by the difference in transition probabilities obtained from NA-TST and fewest switches molecular dynamics, and it is believed to be a result of the NA-TST semilocal description of nonadiabatic transitions in the vicinity of the intersystem crossing. Also, the larger triplet state lifetime obtained from NA-TST could be a result of the quantum sampling of rovibrational states, which is missing in classical trajectories traversing the crossing seam.

Nonadiabatic transition state theory: Application to intersystem crossings in the active sites of metal‐sulfur proteins

“…In general, there is no reason to assume that a reaction trajectory crosses the seam surface only twice, or that it always proceeds through the MECP. The nonadiabatic molecular dynamics simulations indicate that many crossings can take place before transition occurs, and show that transitions can happen away from the MECP . In principle, such nonlocal effects can be accounted for by sampling PESs near the crossing seam with Monte Carlo method or short molecular dynamics trajectories .…”

“…In principle, the rates of intersystem crossings can be calculated by solving the quantum Schrödinger or classical Newton equations for the nuclear motion on the multiple coupled electronic PESs using nonadiabatic ab initio molecular dynamics (NA‐AIMD). In the most of the applications of NA‐AIMD to intersystem crossings, the classical nuclear trajectories are propagated on the PESs prebuild or calculated “on the‐fly” along the nuclear trajectories . The last approach, also called direct dynamics , can be applied to relatively large systems with dozens of atoms.…”

Detection and characterization of singly deuterated silylene, SiHD, via optical spectroscopy

“…Modelling the role of SiH 2 in the fabrication of amorphous silicon thin films and polycrystalline silicon has also attracted significant interest. [1][2][3][4][5][6] Motivated primarily by the desire to garner a fundamental understanding of the properties of this simplest of silicon containing polyatomic molecules, and in part by the desire to develop a real time, in situ SiH 2 monitoring scheme, there have been numerous reported experimental and theoretical [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] studies of gas-phase SiH 2 , and to a lesser extent SiD 2 . In addition, SiH 2 is predicted to be abundant in circumstellar envelopes of carbon rich stars 49 and has been tentatively identified 50,51 via the detection of the 1 11 -0 00 pure rotational transition.…”

“…28 The spectra were interpreted as quasilinear behavior in theB 1 A 1 state with a very small barrier ( 125 cm −1 ) to linearity. Now turning to the theoretical studies, there have been numerous ab initio predictions of the properties of SiH 2 , with particular emphasis on understanding the state ordering [29][30][31][32][33][34][35][39][40][41][42]47 relative to that of CH 2 , to gain insight into the unimolecular dynamics, 36,46,48 and aid in the interpretation of the spectra. 37,[43][44][45][46] In addition to these electronic structure prediction, Duxbury et al 38 reanalyzed the originally recorded X 1 A 1 →à 1 B 1 absorption spectra of SiH 2 7,8 and rationalized the strong local perturbations and observed anomalous radiative lifetimes 14 43 In that study, ab initio calculations of the potential energy surfaces (PESs), the electric dipole moments, and the electric dipole transition moment surfaces for theX 1 A 1 andà 1 B 1 were performed.…”

Constructing spin‐adiabatic states for the modeling of spin‐crossing reactions. I. A shared‐orbital implementation

“…The rate of a spin-crossing reaction is then assessed from the energy required to reach the MECP (ie, activation energy) as well as the SOC value at the MECP (which controls the probability to cross onto another spin-diabatic state). [17,19,20] The spin-adiabatic approach, [3,21] on the other hand, has gained a lot of momentum in the last couple of years. [1,3,4,7,16] One can further study the transition rate between different spin-diabatic states by including SOC in nonadiabatic transition state (TS) theory simulations [17,18] or surface hopping dynamics.…”