An automated predictor for identifying transition states in solids

Abstract

The minimum energy path (MEP) and transition state are two key parameters in the investigation of the mechanisms of chemical reactions and structural phase transformations. However, determination of transition paths in solids is challenging. Here, we present an evolutionary method to search for the lowest energy path and the transition state for pressure-induced structural transformations in solids without any user input or prior knowledge of possible paths. Instead, the initial paths are chosen stochastically by connecting randomly selected atoms from the initial to final structure. The MEP of these trials paths were computed and ranked in order of their energies. The matrix particle swarm optimization algorithm is then used to generate improved transition paths. The procedure is repeated until the lowest energy MEP is found. This method is validated by reproducing results of several known systems. The new method also successfully located the MEP for the direct low-temperature pressure induced transformation of face centered-cubic (FCC) silicon to the simple hexagonal(sh) phase and FCC lithium to a complex body centered-cubic cI16 high-pressure phase. The proposed method provides a convenient, robust, and reliable approach to identify the MEP of phase transformations. The method is general and applicable to a variety of problems requiring the location of the transition state.

A mechanism for aragonite to post-aragonite transition in MCO3 (M = Ca, Sr and Ba) carbonates: evidence of a hidden metastable polymorph

“…28 Although several automatic procedures have been recently developed to explore crystal PESs and evaluate minimal energy paths (see for example ref. [29][30][31], we believe that a symmetry analysis of group-subgroup relationships applied to carbonate structures is still indispensable to envisage chemically founded transition pathways. This approach is especially necessary if many degrees of freedom are present as in the polymorphic sequence of carbonates, where multi-step mechanisms are expected along the transformations.…”

Cesium-mediated electron redistribution and electron-electron interaction in high-pressure metallic CsPbI3

“…Atomic positions and lattice parameters were relaxed until all the forces on the ions were less than 10 −3 eV/Å. The transition path search was performed by using the evolutionary method implemented in the CALYPSO code 71 . In our calculations, relativistic effects, e.g., spin-orbit coupling (SOC), are not included.…”

Quantum photonics with layered 2D materials

“…The opticallydetected magnetic resonance signal corresponds to a defect with D 3h symmetry, hosting an S=1 electronic spin ground state, with zero-field splitting D~3.5 GHz, and an almost isotropic g-factor g=2. Through electron paramagnetic resonance (EPR) measurements, the defect is identified as an intrinsic defect, the negativelycharged boron vacancy V B (-) 163 . The zero-field splitting shows a quite strong temperature dependence (changing of ~120 MHz between room temperature and 4 K, as opposed to ~7 MHz for the NV centre in diamond), suggesting possible applications in quantum thermometry.…”