Exact Potential Energy Surface Research Articles

Case studies of the time-dependent potential energy surface for dynamics in cavities.

The exact time-dependent potential energy surface driving the nuclear dynamics was recently shown to be a useful tool to understand and interpret the coupling of nuclei, electrons, and photons in cavity settings. Here, we provide a detailed analysis of its structure for exactly solvable systems that model two phenomena: cavity-induced suppression of proton-coupled electron-transfer and its dependence on the initial state, and cavity-induced electronic excitation. We demonstrate the inadequacy of simply using a weighted average of polaritonic surfaces to determine the dynamics. Such a weighted average misses a crucial term that redistributes energy between the nuclear and the polaritonic systems, and this term can in fact become a predominant term in determining the nuclear dynamics when several polaritonic surfaces are involved. Evolving an ensemble of classical trajectories on the exact potential energy surface reproduces the nuclear wavepacket quite accurately, while evolving on the weighted polaritonic surface fails after a short period of time. The implications and prospects for application of mixed quantum-classical methods based on this surface are discussed.

Exact Potential Energy Surface for Molecules in Cavities.

We find and analyze the exact time-dependent potential energy surface driving the proton motion for a model of cavity-induced suppression of proton-coupled electron transfer. We show how, in contrast to the polaritonic surfaces, its features directly correlate to the proton dynamics and we discuss cavity modifications of its structure responsible for the suppression. The results highlight the interplay between nonadiabatic effects from coupling to photons and coupling to electrons and suggest caution is needed when applying traditional dynamics methods based on polaritonic surfaces.

Molecular geometric phase from the exact electron-nuclear factorization

The Born-Oppenheimer electronic wavefunction $\Phi_R^{BO}(r)$ picks up a topological phase factor $\pm 1$, a special case of Berry phase, when it is transported around a conical intersection of two adiabatic potential energy surfaces in $R$-space. We show that this topological quantity reverts to a geometric quantity $e^{i\gamma}$ if the geometric phase $\gamma = \oint \mathrm{Im} \langle \Phi_R |\nabla_{\mu} \Phi_R\rangle \cdot d\mathbf{R}_{\mu}$ is evaluated with the conditional electronic wavefunction $\Phi_R(r)$ from the exact electron-nuclear factorization $\Phi_R(r)\chi(R)$ instead of the adiabatic function $\Phi_R^{BO}(r)$. A model of a pseudorotating molecule, also applicable to dynamical Jahn-Teller ions in bulk crystals, provides the first examples of induced vector potentials and molecular geometric phase from the exact factorization. The induced vector potential gives a contribution to the circulating nuclear current which cannot be removed by a gauge transformation. The exact potential energy surface is calculated and found to contain a term depending on the Fubini-Study metric for the conditional electronic wavefunction.

A study of dynamic properties of exchange reaction H(D)+SH/SD by quasi-classical trajectory method

Sulfur in hydrogen combustion reaction chemistry, which plays an important role in meteorology, combustion reactions, and atmospheric pollution, has been extensively investigated recently. And its reverse reaction has also been a research object gradually. The research in this paper is based on the exact potential energy surface (L S J, Zhang P Y, Han K L, He G Z 2012 J. Chem. Phys. 136 094308), with using the method of quasi-classical trajectory on the exchange reaction of H (D)+SH/SD dynamic properties. In this paper, the scalar properties are calculated, including the cross section, rate constant, opacity function, product vibrational, rotational distributions, product scattering direction, rotational angular momentum orientation, and alignment properties. In this paper, how the collision energy and the isotope affect the reaction H (D)+SH/SD kinetic properties is analyzed in detail. The results show that as collision energy increases, the reaction cross section increases, product backscatter weakens gradually while the product rotational angular momentum alignment and orientation nature strengthen gradually. In addition, the isotope effect has a significant influence on the reaction kinetics. The reaction mechanism which is shown in the title and based on the reaction kinetics and the potential energy surface, is also discussed in this paper.

Is there an exact potential energy surface?

Transition state theory was introduced in the 1930s to account for chemical reactions. Central to this theory is the idea of a potential energy surface (PES). It was assumed that quantum mechanical computation, when it became possible, would yield such surfaces, but for the time being they would have to be constructed empirically. The approach was very successful. Nowadays, quantum mechanical ab initio electronic structure calculations are possible and from their results PESs can be constructed. Such surfaces are now widely used in the explanation of chemical reactions in place of the traditional empirical ones. It is argued here that theoretical basis of such PESs is not quite as clear as is usually assumed and that, from a quantum mechanical perspective, certain puzzles remain.

The muonic He atom and a preliminary study of the reaction

The muonic atom He4μ has the composition α++μ-e-, and is formed by stopping negative muons in He doped with a small amount of NH3 (or Xe). It may be regarded as a unique heavy H-atom isotope with a mass of 4.1 amu. As such, the study of its chemical reaction rates and comparison with those of the well-known light Mu atom (0.113 amu) allows unprecedented tests of kinetic isotope effects over a range of 36 in mass. As a first example, and one which is of most fundamental interest, we have begun kinetics studies of the Heμ+H2→HeμH+H reaction in the gas phase. The first measurements, at 295 K, give a rate constant of kHeμ=4.1±0.7×10-16cm3molec-1s-1. In comparison, variational transition state calculations give a value of 2.46×10-16cm3molec-1s-1, somewhat below the measurement, despite the large error bar, raising the possibility that the calculations, on an essentially exact potential energy surface, have underestimated the amount of quantum tunneling involved, even for this heavy H-atom isotope.