Spin-Density Functional Regularization for Singlet Diradicals.

Broken-symmetry density functional theory (DFT) is one of the commonly used methods for treating the static-correlation effects in singlet diradicals, which arise from the (quasi-)degeneracy of their frontier orbitals. Although the method yields quantitatively accurate energies for simple cases, such as stretched diatomic molecules, it fails for other systems with more complicated electronic structures due to the artificially broken spin symmetries. In this work, we present a spin-density functional regularization (SR) approach within the framework of partition density functional theory (PDFT) to correct errors arising from artificial symmetry breaking in broken-symmetry DFT calculations.

Quantum Disorder Induced by Nuclear Tunneling in Lattice.

Lattice degrees of freedom (d.o.f.

Unveiling interfacial dead layer in wurtzite ferroelectrics.

Wurtzite ferroelectrics hold immense promise to revolutionize modern micro- and nano-electronics due to their compatibility with semiconductor technologies. However, the presence of interfacial dead layers with irreversible polarization limits their development and applications, and the formation mechanisms of dead layers remain unclear. Here, we demonstrate that dead layer formation in ScAlN, a representative wurtzite ferroelectric, originates from a high density of nitrogen vacancies in combination with interfacial strain.

Unveiling the intermediate hydrated proton in water through vibrational analysis on the 1750 cm signature.

Hydration of proton is the key to understand the acid-base chemistry and biochemical processes, for which the Zundel and Eigen cations have been recognized as the foundation. However, their dominance remains contentious due to the challenge of attributing the infrared signature at  ~1750 cm, stemming from the theoretical dilemma of balancing structural diversity and solvent fluctuations. Herein, we circumvent this obstacle by devising an integrated approach for computing frequency-specific vibrational vectors via inverse Fourier transform of the vibrational density of states.

Phonon-Mediated Exciton Relaxation in Two-Dimensional Semiconductors: Selection Rules and Relaxation Pathways.

Exciton-phonon coupling (ExPC) is crucial for energy relaxation in semiconductors, yet the first-principles calculation of such coupling remains challenging, especially for two-dimensional (2D) systems. Here, an accurate method for calculating ExPC is developed and applied in exciton relaxation problems in monolayer WSe. Considering the interplay between the exciton wave functions and electron-phonon coupling (EPC) matrix elements, we find that ExPC shows selection rules distinct from the ones of EPC.

Robust Gaussian Process Regression Method for Efficient Tunneling Pathway Optimization: Application to Surface Processes.

Simulation of surface processes is a key part of computational chemistry that offers atomic-scale insights into mechanisms of heterogeneous catalysis, diffusion dynamics, and quantum tunneling phenomena. The most common theoretical approaches involve optimization of reaction pathways, including semiclassical tunneling pathways (called instantons). The computational effort can be demanding, especially for instanton optimizations with an ab initio electronic structure.

Complex phase diagram and supercritical matter.

The supercritical region is often described as uniform with no definite transitions. The distinct behaviors of the matter therein, e.g.

Accurate calculation of tunneling splittings in water clusters using path-integral based methods.

Tunneling splittings observed in molecular rovibrational spectra are significant evidence for tunneling motion of hydrogen nuclei in water clusters. Accurate calculations of the splitting sizes from first principles require a combination of high-quality inter-atomic interactions and rigorous methods to treat the nuclei with quantum mechanics. Many theoretical efforts have been made in recent decades.

Torsional Tunneling Splitting in a Water Trimer.

Using a full-dimensional quantum method for nuclei and a new first-principles water potential, we show that the torsional tunneling splitting in a water trimer can be reproduced with accuracy up to ∼1 cm. We quantify the coupling constants of the nuclear quantum states between nonadjacent wells and show that they are the main reason for shifting the quartet-split levels in spectra from a 1:2:1 spacing. This demonstrates the limitation of treatments using simplified models such as the Hückel model and emphasizes the nonlocal nature of the quantum interactions in this system.

Ultrafast charge transfer coupled to quantum proton motion at molecule/metal oxide interface.

Understanding how the nuclear quantum effects (NQEs) in the hydrogen bond (H-bond) network influence the photoexcited charge transfer at semiconductor/molecule interface is a challenging problem. By combining two kinds of emerging molecular dynamics methods at the ab initio level, the path integral-based molecular dynamics and time-dependent nonadiabatic molecular dynamics, and choosing CHOH/TiO as a prototypical system to study, we find that the quantum proton motion in the H-bond network is strongly coupled with the ultrafast photoexcited charge dynamics at the interface. The hole trapping ability of the adsorbed methanol molecule is notably enhanced by the NQEs, and thus, it behaves as a hole scavenger on titanium dioxide.

Determination of concerted or stepwise mechanism of hydrogen tunneling from isotope effects: Departure between experiment and theory.

Isotope substitution is an important experimental technique that offers deep insight into reaction mechanisms, as the measured kinetic isotope effects (KIEs) can be directly compared with theory. For multiple proton transfer processes, there are two types of mechanisms: stepwise transfer and concerted transfer. The Bell-Limbach model provides a simple theory to determine whether the proton transfer mechanism is stepwise or concerted from KIEs.

Dynamic Nature of High-Pressure Ice VII.

Starting from Shannon's definition of dynamic entropy, we propose a theory to describe the rare-event-determined dynamic states in condensed matter and their transitions and apply it to high-pressure ice VII. A dynamic intensive quantity named dynamic field, rather than the conventional thermodynamic intensive quantities such as temperature and pressure, is taken as the controlling variable. The dynamic entropy versus dynamic field curve demonstrates two dynamic states in the stability region of ice VII and dynamic ice VII.