Even three decades after signing the Chemical Weapons Convention, organophosphorus chemical warfare agents (CWAs), such as sarin, remain a threat. The development of novel methods for the detection of CWAs, protection from CWAs, and CWA decontamination motivates research on their physicochemical properties. Due to the extreme toxicity of sarin, most of the experimental studies are carried out using less toxic simulant compounds. In addition to experimental studies of sarin simulants, both sarin and simulants can be studied using in silico experimentsmolecular simulations. The results of classical molecular modeling of the compounds and their agreement with experimental data rely on the force field used to describe the system. In recent years, there have been several force fields proposed for sarin and its most common simulant dimethyl methylphosphonate (DMMP). However, other simulants frequently used in experiments received less attention from the molecular simulation perspective, for example, to date, there is no force field and no simulation data for diisopropyl methylphosphonate (DIMP). Here, we compare the literature force fields for sarin and DMMP, focusing specifically on the vapor–liquid equilibrium for the pure species. We carried out Monte Carlo and molecular dynamics simulations using the existing literature force fields from which we predicted the liquid densities and vapor pressures developing the entire binodal curves. We compared the predictions to the experimental data and showed that the TraPPE-UA force field outperformed the other force fields. Thus, we extended TraPPE-UA for DIMP, utilized this force field in molecular simulations, and predicted the liquid densities and vapor pressures for a range of temperatures (binodal curve), which agreed well with the published experimental data. From the binodal, we calculated the critical properties of DIMP and demonstrated that these parameters can be used in the Peng–Robinson equation of state for this compound.
Modeling the dynamics of non-bound states in molecules requires an accurate description of how electronic motion affects nuclear motion and vice-versa. The exact factorization (XF) approach offers a unique perspective, in that it provides potentials that act on the nuclear subsystem or electronic subsystem, which contain the effects of the coupling to the other subsystem in an exact way. We briefly review the various applications of the XF idea in different realms, and how features of these potentials aid in the interpretation of two different laser-driven dissociation mechanisms. We present a detailed study of the different ways the coupling terms in recently-developed XF-based mixed quantum-classical approximations are evaluated, where either truly coupled trajectories, or auxiliary trajectories that mimic the coupling are used, and discuss their effect in both a surface-hopping framework as well as the rigorously-derived coupled-trajectory mixed quantum-classical approach.
The coupled-trajectory mixed quantum–classical method (CTMQC), derived from the exact factorization approach, has successfully predicted photo-chemical dynamics in a number of interesting molecules, capturing population transfer and decoherence from first principles. However, due to the approximations made, CTMQC does not guarantee energy conservation. We propose a modified algorithm, CTMQC-E, which redefines the integrated force in the coupled-trajectory term so to restore energy conservation, and demonstrate its accuracy on scattering in Tully’s extended coupling region model and photoisomerization in a retinal chromophore model.
Metal nanoparticles have been of interest to the field of nanomedicine due to their potential for cancer treatment, diagnosis, and antimicrobial activity. Particularly, platinum nanoparticles (PtNPs) have been reported to...
Modeling the dynamics of non-bound states in molecules requires an accurate description of how electronic motion affects nuclear motion and vice-versa. The exact factorization (XF) approach offers a unique perspective, in that it provides potentials that act on the nuclear subsystem or electronic subsystem, which contain the effects of the coupling to the other subsystem in an exact way. We briefly review the various applications of the XF idea in different realms, and how features of these potentials aid in the interpretation of two different laser-driven dissociation mechanisms.We present a detailed study of the different ways the coupling terms in recently-developed XF-based mixed quantum-classical approximations are evaluated, where either truly coupled trajectories, or auxiliary trajectories that mimic the coupling are used, and discuss their effect in both a surfacehopping framework as well as the rigorously-derived coupled-trajectory mixed quantum-classical approach.
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