Global Search for Structures of Carbon Crystal Under Ultrahigh Pressure

In this study, a systematic search for structures of carbon crystal under ultrahigh pressure was performed by using the artificial force induced reaction method including periodic boundary conditions (PBC/SC-AFIR). To perform a search under an arbitrary pressure, an algorithm to take account of pressure was implemented in the GRRM program. At 100 GPa, the search generated 710 unique structures automatically. These structures were compared with 982 structures obtained by the search under zero pressure. The structures at 100 GPa were much denser than those under zero pressure. Besides, new structures that were denser than diamond were obtained at 100 GPa

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

Artificial Force Induced Reaction (AFIR) Method for Exploring Quantum Chemical Potential Energy Surfaces

In this account, a technical overview of the artificial force induced reaction (AFIR) method is presented. The AFIR method is one of the automated reaction-path search methods developed by the authors, and has been applied extensively to a variety of chemical reactions, such as organocatalysis, organometallic catalysis, and photoreactions. There are two modes in the AFIR method, i.e., a multicomponent mode and a single-component mode. The former has been applied to bimolecular and multicomponent reactions and the latter to unimolecular isomerization and dissociation reactions. Five numerical examples are presented for an Aldol reaction, a Claisen rearrangement, a Co-catalyzed hydroformylation, a fullerene structure search, and a nonradiative decay path search in an electronically excited naphthalene molecule. Finally, possible applications of the AFIR method are discussed

Global search for low-lying crystal structures using the artificial force induced reaction method : A case study on carbon

We propose an approach to perform the global search for low-lying crystal structures from first principles, by combining the artificial force induced reaction (AFIR) method and the periodic boundary conditions (PBCs). The AFIR method has been applied extensively to molecular systems to elucidate the mechanism of chemical reactions such as homogeneous catalysis. The present PBC/AFIR approach found 274 local minima for carbon crystals in the C-8 unit cell described by the generalized gradient approximation-Perdew-Burke-Ernzerhof functional. Among many newly predicted structures, three low-lying structures, which exhibit somewhat higher energy compared with those previously predicted, such as Cco-C-8 (Z-carbon) and M-carbon, are further discussed with calculations of phonon and band dispersion curves. Furthermore, approaches to systematically explore two- or one-dimensional periodic structures are proposed and applied to the C-8 unit cell with the slab model. These results suggest that the present approach is highly promising for predicting crystal structures

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