arXiv subjects

Wenbin Fan

Publications and source records attributed to Wenbin Fan.

3 recordsLinked to original sources

arXiv2022

New Stable and Fast Ring-Polymer Molecular Dynamics for Calculating Bimolecular Rate Coefficients with Example of OH + CH_4

The accurate and efficient calculation of the rate coefficients of chemical reactions is a key issue in the research of chemical dynamics. In this work, by applying the dimension-free ultra-stable Cayley propagator, the thermal rate coefficients of a prototypic high dimensional chemical reaction OH + CH4 -> H2O + CH3 in the temperature range of 200 K to 1500 K are investigated with ring polymer molecular dynamics (RPMD), on a highly accurate full-dimensional potential energy surface. Kinetic isotope effects (KIEs) for three isotopologues of the title reaction are also studied. The results demonstrate excellent agreement with experimental data, even in the deep tunneling region. Especially, the Cayley propagator shows high calculation efficiency with little loss of accuracy. The present results confirmed the applicability of the RPMD method, particularly the speed-up by Cayley propagator, in theoretical calculations of bimolecular reaction rates.

physics.chem-ph↗

arXiv2021

Mechanisms of Molecular Ferroelectrics Made Simple

Molecular ferroelectrics have captured immense attention due to their superiority over inorganic oxide ferroelectrics, such as environmentally friendly, low-cost, flexible, foldable. However, the mechanisms of ferroelectric switching and phase transition for the molecular ferroelectrics are still missing, leaving the development of novel molecular ferroelectrics less efficient. In this work, we have provided a methodology combining molecular dynamics (MD) simulation on a polarized force field named polarized crystal charge (PCC) and enhanced sampling technique, replica-exchange molecular dynamics (REMD) to simulate such mechanisms. With this procedure, we have investigated a promising molecular ferroelectric material, (R)/(S)-3-quinuclidinol crystal. We have simulated the ferroelectric hysteresis loops of both enantiomers and obtained spontaneous polarization of 7/8 \mu C cm-2 and a corresponding coercive electric field of 15 kV cm-1. We also find the Curie temperature as 380/385 K for ferro-/para-electric phase transition of both enantiomers. All of the simulated results are highly compatible with experimental values. Besides of that, we predict a novel Curie temperature of about 600 K. This finding is further validated by principal component analysis (PCA). Our work would significantly promote the future exploration of multifunctional molecular ferroelectrics for the next generation of intelligent devices.

physics.chem-ph↗

arXiv2020

Rate coefficients of a roaming reaction H + MgH using the ring polymer molecular dynamics

The ring-polymer molecular dynamics (RPMD) was used to calculate the thermal rate coefficients of the two-channel roaming reaction H + MgH. Both reaction channels, tight and roaming, are explicitly considered. This is a pioneering attempt of exerting RPMD method to multi-channel reactions. With the help of a newly developed optimization-interpolation protocol for preparing the initial structures and adaptive protocol for choosing the force constants, we have successfully obtained the thermal rate coefficients. The results are consistent with those from other theoretical methods, such as variational transition state theory (VTST) and quantum dynamics (QD). Especially, RPMD results exhibit negative temperature dependence, which is similar to results from VTST but different from ones from ground state QD calculations.

physics.chem-ph↗