Ultrafast X-ray Scattering from Molecules

We present a theoretical framework for the analysis of ultrafast X-ray scattering experiments using nonadiabatic quantum molecular dynamics simulations of photochemical dynamics. A detailed simulation of a pump-probe experiment in ethylene is used to examine the sensitivity of the scattering signal to simulation parameters. The results are robust with respect to the number of wavepackets included in the total expansion of the molecular wave function. Overall, the calculated scattering signals correlate closely with the dynamics of the molecule

Comparison of ultrafast electron and X-ray diffraction - a computational study

We compare ultrafast electron and X-ray diffraction using quantum molecular dynamics simulations in photoexcited ethylene. The simulations of ethylene are done using the ab-initio multiconfigurational Ehrenfest (AI-MCE) approach, with electronic structure calculations at the SA3-CASSCF(2,2)/cc-ppVDZ level. The diffraction signal is calculated using the independent atom model. We find that the electron diffraction is more sensitive the dynamics of the hydrogen atoms in the molecule

Simulation of ultrafast photodynamics of pyrrole with a multiconfigurational Ehrenfest method

We report the first results of ab initio multiconfigurational Ehrenfest simulations of pyrrole photodynamics. We note that, in addition to the two intersections of 11A2 and 11B1 states with the ground state 11A1, which are known to be responsible for N–H bond fission, another intersection between the 12A2 and 12B1 states of the resulting molecular radical becomes important after the departure of the H atom. This intersection, which is effectively between the two lowest electronic states of the pyrrolyl radical, may play a significant role in explaining the branching ratio between the two states observed experimentally. The exchange of population between the two states of pyrrolyl occurs on a longer scale than that of N–H bond fission

Study protocol for a multi-center, randomized controlled trial to develop Japanese denture adhesive guidelines for patients with complete dentures : the Denture Adhesive Guideline trial : study protocol for a randomized controlled trial

Background: Denture adhesives, characterized as medical products in 1935 by the American Dental Association, have been considered useful adjuncts for improving denture retention and stability. However, many dentists in Japan are hesitant to acknowledge denture adhesives in daily practice because of the stereotype that dentures should be inherently stable, without the aid of adhesives. The aim of this study is to verify the efficacy of denture adhesives to establish guidelines for Japanese users. The null hypothesis is that the application of denture adhesives, including the cream and powder types, or a control (isotonic sodium chloride solution) would not produce different outcomes nor would they differentially improve the set outcomes between baseline and day 4 post-application. Methods: This ten-center, randomized controlled trial with parallel groups is ongoing. Three hundred edentulous patients with complete dentures will be allocated to three groups (cream-type adhesive, powder-type adhesive, and control groups). The participants will wear their dentures with the denture adhesive for 4 days, including during eight meals (three breakfasts, two lunches, and three dinners). The baseline measurements and final measurements for the denture adhesives will be performed on the first day and after breakfast on the fourth day. The primary outcome is a general satisfaction rating for the denture. The secondary outcomes are denture satisfaction ratings for various denture functions, occlusal bite force, resistance to dislodgement, masticatory performance, perceived chewing ability, and oral health-related quality of life. Between-subjects comparisons among the three groups and within-subjects comparisons of the pre- and post-intervention measurements will be performed. Furthermore, a multiple regression analysis will be performed. The main analyses will be based on the intention-to-treat principle. A sample size of 100 subjects per group, including an assumed dropout rate of 10 %, will be required to achieve 80 % power with a 5 % alpha level. Discussion: This randomized clinical trial will provide information about denture adhesives to complete denture wearers, prosthodontic educators, and dentists in Japan. We believe this new evidence on denture adhesive use from Japan will aid dentists in their daily practice even in other countries

An energy decomposition and extrapolation scheme for evaluating electron transfer rate constants: A case study on electron self-exchange reactions of transition metal complexes

A simple approach for analyzing electron transfer (ET) reactions is proposed based on energy decomposition and extrapolation schemes. The present energy decomposition and extrapolation-based electron localization (EDEEL) method represents the diabatic energies for the initial and final states using the adiabatic energies of the donor and acceptor species and their complex. A scheme to estimate ET rate constants efficiently is also proposed by combining it with the Marcus theory. EDEEL is semi-quantitative by directly evaluating the seam-of-crossing region of two diabatic potentials. In a numerical test, EDEEL successfully provided ET rate constants for electron self-exchange reactions of thirteen transition metal complexes with reasonable accuracy. Furthermore, its energy decomposition and extrapolation schemes give all the energy values required in the activation strain model (ASM) analysis. The ASM analysis using EDEEL provided rational interpretations of the variation of the ET rate constants depending on the transition metal complexes. Its extension combining two computational levels was discussed to further reduce its computational costs. These results suggest that EDEEL is useful in efficiently evaluating ET rate constants and obtaining a rational understanding of their magnitudes

Understanding CO oxidation on the Pt(111) surface based on a reaction route network

Analysis of a reaction on a solid surface is an important task for understanding the catalytic reaction mechanism. In this study, we studied CO oxidation on the Pt(111) surface by using the artificial force induced reaction (AFIR) method. A systematic reaction path search was done, and the reaction route network was created. This network included not only bond rearrangement paths but also migration paths of adsorbed species. Then, the obtained network was analyzed using a kinetics method called rate constant matrix contraction (RCMC). It is found that the bottleneck of the overall reaction is the CO2 generation step from an adsorbed CO molecule and an O atom. This result is consistent with the Langmuir-Hinshelwood (LH) mechanism with O-2 dissociation discussed in previous studies. The present procedure, i.e., construction of the reaction route network by the AFIR method followed by application of the RCMC kinetics method to the resultant reaction route network, was fully systematic and uncovered two aspects: the impact of the existence of multiple paths in each bond rearrangement step and an entropic contribution arising from short-range migration of adsorbed species

Theoretical study on mechanism of the photochemical ligand substitution of fac-[Re-I(bpy)(CO)(3)(PR3)](+) complex

The mechanism of the CO ligand dissociation of fac-[Re-I(bpy)(CO)(3)P(OMe)(3)](+) has theoretically been investigated, as the dominant process of the photochemical ligand substitution (PLS) reactions of fac-[Re-I(bpy)(CO)(3)PR3](+), by using the (TD-)DFT method. The PLS reactivity can be determined by the topology of the T-1 potential energy surface because the photoexcited complex is able to decay into the T-1 state by internal conversions (through conical intersections) and intersystem crossings (via crossing seams) with sufficiently low energy barriers. The T-1 state has a character of the metal-to-ligand charge-transfer ((MLCT)-M-3) around the Franck-Condon region, and it changes to the metal-centered ((MC)-M-3) state as the Re-CO bond is elongated and bent. The equatorial CO ligand has a much higher energy barrier to leave than that of the axial CO, so that the axial CO ligand selectively dissociates in the PLS reaction. The single-component artificial force induced reaction (SC-AFIR) search reveals the CO dissociation pathway in photostable fac-[ReI(bpy)(CO)(3)Cl]; however, the dissociation barrier on the T-1 state is substantially higher than that in fac-[ReI(bpy)(CO)(3)PR3](+) and the minimum-energy seams of crossings (MESXs) are located before and below the barrier. The MESXs have also been searched in fac-[Re-I(bpy)(CO)(3)PR3](+) and no MESXs were found before and below the barrier

Computational searches for crystal structures of dioxides of group 14 elements (CO2, SiO2, GeO2) under ultrahigh pressure

In this study, we focused on the effect of pressure on the crystal structures of dioxides of group 14 elements,i.e.SiO2, GeO2, and CO2. Systematic searches for their crystal structures using the artificial force induced reaction method generated 219 and 147, 102 and 63, and 148 and 76 structures for SiO2, GeO2, and CO2, respectively, at 1 and 10(6)atm. At 1 atm, cristobalite-like, quartz, anatase-like, and stishovite were stable structures for SiO(2)and GeO2. At 10(6)atm, structures of stishovite and CaCl(2)type were relatively stable for SiO(2)and GeO2. At 1 atm of CO2, molecular crystals were the most stable, whereas, quartz-like and cristobalite-like structures were obtained as stable structures at 10(6)atm. We discuss these pressure dependent structural variations systematically using the obtained structural dataset