Quantitative Modeling of Excited-State Dynamics in Valence Photoionized Vinyl Fluoride.

Long-standing debates regarding the dissociative photoionization of vinyl fluoride (fluoroethene) were resolved using large-scale surface-hopping ab initio molecular dynamics (SH-AIMD) simulations. By combining accurate initial condition sampling, electronic cross-section calculations, and SH-AIMD with density functional theory (DFT) and complete active space second-order perturbation theory (CASPT2), we obtained not only qualitative insight into excited-state dynamics but also quantitatively accurate predictions of the photoelectron spectrum, fluorine-loss branching ratios, and translational kinetic energy release distributions for F + CH products. Statistical dissociation arises from the A″- A' states, while, in the A″- A' states, excited-state dissociation within 50-250 fs dominates.

Series expansion of a scalable Hermitian excitonic renormalization method.

Utilizing the sparsity of the electronic structure problem, fragmentation methods have been researched for decades with great success, pushing the limits of ab initio quantum chemistry ever further. Recently, this set of methods has been expanded to include a fundamentally different approach called excitonic renormalization, providing promising initial results. It builds a supersystem Hamiltonian in a second-quantized-like representation from transition-density tensors of isolated fragments, contracted with biorthogonalized molecular integrals.

Ultrafast charge separation driven by differential particle and hole mobilities.

The process of a local excitation evolving into an intramolecular charge-separated state is followed and compared for several systems by directly simulating the time propagation of the electronic wavefunction. The wavefunction and Hamiltonian are handled using the extended second-order algebraic diagrammatic construction (ADC(2)-x), which explicitly accounts for electron correlation in the dynamic many-particle state. The details of the charge separation can be manipulated according to the chemical composition of the system; atoms which dope the conjugated system with either particles or holes are shown to effect whether the particle or hole is more mobile.

A study of the effect of attenuation curvature on molecular correlation energies by introducing an explicit cutoff radius into two-electron integrals.

We present a new attenuator function that can be applied to the Coulomb operator. Similar to the popular erf(omegar) attenuator, the function [erf(omega(r + r0)) + erf(omega(r - r0))]/2 divides the Coulomb potential into a singular short-range piece and a non-singular long-range piece. In our attenuator, omega controls the sharpness of the short-range/long-range division at r0.

Fast localized orthonormal virtual orbitals which depend smoothly on nuclear coordinates.

We present here an algorithm for computing stable, well-defined localized orthonormal virtual orbitals which depend smoothly on nuclear coordinates. The algorithm is very fast, limited only by diagonalization of two matrices with dimension the size of the number of virtual orbitals. Furthermore, we require no more than quadratic (in the number of electrons) storage.

Simulated quantum computation of molecular energies.

The calculation time for the energy of atoms and molecules scales exponentially with system size on a classical computer but polynomially using quantum algorithms. We demonstrate that such algorithms can be applied to problems of chemical interest using modest numbers of quantum bits. Calculations of the water and lithium hydride molecular ground-state energies have been carried out on a quantum computer simulator using a recursive phase-estimation algorithm.

Scaled opposite-spin second order Møller-Plesset correlation energy: an economical electronic structure method.

A simplified approach to treating the electron correlation energy is suggested in which only the alpha-beta component of the second order Møller-Plesset energy is evaluated, and then scaled by an empirical factor which is suggested to be 1.3. This scaled opposite-spin second order energy (SOS-MP2), where MP2 is Møller-Plesset theory, yields results for relative energies and derivative properties that are statistically improved over the conventional MP2 method.