Transient Changes in Molecular Geometries and How to Model Them

Solution Structure and Ultrafast Vibrational Relaxation of the PtPOP Complex Revealed by ΔSCF-QM/MM Direct Dynamics Simulations

“…Broadly speaking, much of the efforts of the theoretical community to address this problem have been directed towards the development and application of two computational frameworks of choice: methods that solve the time-dependent Schrödinger equation for the nuclei using precomputed potential energy surfaces (PESs), [17][18][19][20][21][22][23] and methods based on classical propagation of the nuclei with on-thefly evaluation of energies and forces at ab initio level. [24][25][26][27][28][29][30][31][32][33] Quantum dynamics approaches have proven useful in deciphering some aspects of the excited-state decay pathways of photocatalytic metal complexes, particularly concerning non-adiabatic electronic transitions. 17,20 However, the outcome of this kind of simulation relies on the selection of a small number of vibrational modes along which the dynamics is restricted.…”

“…One of the main challenges associated with the a priori determination of the mechanisms of the ultrafast excited-state dynamics of complex molecular systems is represented by the time scales one is able to simulate while retaining accuracy. Broadly speaking, much of the efforts of the theoretical community to address this problem have been directed toward the development and application of two computational frameworks of choice: methods that solve the time-dependent Schrödinger equation for the nuclei using precomputed potential energy surfaces (PESs) − and methods based on classical propagation of the nuclei with on-the-fly evaluation of energies and forces at ab initio level. − Quantum dynamics approaches have proven useful in deciphering some aspects of the excited-state decay pathways of photocatalytic metal complexes, particularly concerning nonadiabatic electronic transitions. , However, the outcome of this kind of simulation relies on the selection of a small number of vibrational modes along which the dynamics is restricted. Furthermore, solvent effects in quantum wave packet simulations are usually accounted for in an implicit manner, , thus neglecting any explicit solvation dynamics effect.…”

Ultrafast X-ray absorption study of longitudinal–transverse phonon coupling in electrolyte aqueous solution

“…The 10 simulation boxes were then re-equilibrated using electrostatically embedded QM/MM MD. [21][22][23] The ion is modelled with the same parameters as in the structural relaxation, apart from the addition of non-bonded force field parameters needed for the additive QM/MM MD scheme, and a larger grid spacing of 0.18 Å, to increase the computational efficiency, and since so-called 'eggbox-effects' of the real space grid (small changes in energy and forces with respect to atomic positions relative to grid points) will average out in the thermal sampling. The parameters were taken from the UFF force field.…”

Electron Transfer and Solvent-Mediated Electronic Localization in Molecular Photocatalysis

“…We have recently addressed this by developing a fast implementation of a DFT-based, QM/MM BOMD method [23][24][25] . Utilizing the efficiency of a real-space implementation of the Projector Augmented Wave (PAW) method, [26][27][28] it is possible to rapidly and robustly model photoactive complexes comprised of up to hundreds of atoms, their environments, and to make it computationally viable to produce multiple-trajectory statistics for more reliable comparisons to experimental data.…”

“…One way of addressing these shortcomings is by interfacing quantum mechanical calculations with explicit solvent molecules described within a molecular mechanics framework (QM/MM calculations) and propagating the system under ambient conditions, using molecular dynamics (MD). − However, simulations within this type of framework are very costly, since the electronic density must be fully reconverged for every classical time step (Born–Oppenheimer MD, BOMD), or the time steps must be very small (Carr–Parrinello MD), either way resulting in a reduction in the generality of the findings from such frameworks. We recently addressed this by developing a fast implementation of a density functional theory (DFT)-based, QM/MM BOMD method. − Utilizing the efficiency of a real-space implementation of the Projector Augmented Wave (PAW) method, − it is possible to rapidly and robustly model photoactive complexes comprised of up to hundreds of atoms, their environments, and to make it computationally viable to produce multiple-trajectory statistics for more reliable comparisons to experimental data.…”