arXiv subjects

Wooil Yang

Publications and source records attributed to Wooil Yang.

11 recordsLinked to original sources

arXiv2026

First-principles carrier mobility and optical absorption of strained ZnO with self-consistent Hubbard interactions

Carrier mobility and optical absorption are key performance parameters of oxide semiconductors in transparent and flexible displays. We use a newly developed density-functional perturbation theory with a self-consistent Hubbard correction (DFPT+U) to study phonon-limited electron transport and phonon-assisted optical absorption in strained zinc oxide (ZnO). This parameter-free approach accounts for electron-phonon interactions and on-site correlation effects simultaneously. Electronic structures and phonon dispersions are computed under three distinct uniaxial strain directions. Uniaxial tensile strain up to 4.8% along [\bar110] is found to increase the room-temperature electron mobility by 19% while leaving visible-range optical absorption essentially unchanged. These results demonstrate that moderate strain can selectively enhance carrier transport without degrading optical transparency, and establish DFPT+U as an effective framework for predicting strain-dependent transport and optical properties in wide-band-gap oxides with implications for strain-engineered display and optoelectronic applications.

cond-mat.mtrl-sci↗

arXiv2026

Robust and Interpretable Adaptation of Equivariant Materials Foundation Models via Sparsity-promoting Fine-tuning

Pre-trained materials foundation models, or machine learning interatomic potentials, leverage general physicochemical knowledge to effectively approximate potential energy surfaces. However, they often require domain-specific calibration due to physicochemical diversity as well as mismatches between practical computational settings and those used in constructing the pre-training data. To address this, we propose a sparsity-promoting fine-tuning method that selectively updates model parameters by exploiting the structural properties of E(3)-equivariant materials foundation models. On energy and force prediction tasks across molecular and crystalline benchmarks, our method matches or surpasses full fine-tuning and equivariant low-rank adaptation while updating only $\sim$3~\% of parameters, and in some cases as little as $\sim$0.5~\%. Beyond energy and force calibration, we further demonstrate task generalizability by applying our method to magnetic moment prediction and magnetism-aware total energy modeling. Finally, analysis of sparsity patterns reveals physically interpretable signatures, such as enhanced $d$-orbital contributions in transition metal systems. Overall, our results establish sparsity-promoting fine-tuning as a flexible and interpretable method for domain specialization of equivariant materials foundation models.

cs.LG↗

arXiv2025

Comparing Hubbard parameters from linear-response theory and Hartree-Fock-based approach

Density-functional theory with on-site $U$ and inter-site $V$ Hubbard corrections (DFT+$U$+$V$) is a powerful and accurate method for predicting various properties of transition-metal compounds. However, its accuracy depends critically on the values of these Hubbard parameters. Although they can be determined empirically, first-principles methods provide a more consistent and reliable approach; yet, their results can vary, and a comprehensive comparison between methods is still lacking. Here, we present a systematic comparison of two widely used approaches for computing $U$ and $V$, namely linear-response theory (LRT) and the Hartree-Fock-based pseudohybrid functional formalism, applied to a representative set of oxides (MnO, NiO, CoO, FeO, BaTiO$_3$, ZnO, and ZrO$_2$). We find that for partially occupied transition-metal $d$ states, these two methods yield consistent $U$ values, but they differ for nearly empty or fully filled $d$ shells. For O-$2p$ states, LRT always predicts large $U$ values ($\sim$10 eV), whereas the pseudohybrid formalism produces system-dependent values depending on the level of localization and hybridization for the electronic states. Even larger differences are found for the inter-site $V$: the former predicts consistently small values ($<1$ eV), while the latter produces larger values ($\sim3$ eV), reflecting its explicit dependence on relative charge redistribution. Our results show that while parallels between these two methods exist, they rely on distinct assumptions for determining $U$ and $V$, leading to variations in predictions of material properties.

cond-mat.mtrl-sci↗

arXiv2025

First-principles electron-phonon interactions with self-consistent Hubbard interaction: an application to transparent conductive oxides

The ab initio computational method known as Hubbard-corrected density functional theory (DFT+$U$) captures well ground electronic structures of a set of solids that are poorly described by standard DFT alone. Since lattice dynamical properties are closely linked to electronic structures, the Hubbard-corrected density functional perturbation theory (DFPT+$U$) can calculate them at the same level of accuracy. To investigate the effects of $U$ on electron-phonon (el-ph) interactions, we implemented DFPT+$U$ with a Hartree-Fock-based pseudohybrid functional formalism to determine $U$ self-consistently and applied our method to compute optical and transport properties of transparent conductive oxides of CdO and ZnO. For CdO, we find that opening a band gap due to $U$ restores the long-range Fr\"ohlich interaction and that its calculated mobility and absorption spectrum are in excellent agreement with experiments. For ZnO where a band gap already appears at the DFT level, DFPT+$U$ brings the results into much closer alignment with experiment, thus demonstrating improved accuracy of our method in dealing with el-ph interactions in these technologically important materials.

cond-mat.mtrl-sci↗

arXiv2025

First-principles study of dielectric properties of ferroelectric perovskite oxides with on-site and inter-site Hubbard interactions

We study the atomic and electronic structures of ferroelectric perovskite oxides, BaTiO$_3$, LiNbO$_3$, and PbTiO$_3$ using ab initio extended Hubbard functionals in which the on-site and inter-site Hubbard interactions are determined self-consistently, adapted from the pseudohybrid density functional proposed by Agapito-Curtarolo-Buongiorno Nardelli. Band structures, ferroelectric distortions, polarization, Born effective charges, and switching barriers are calculated with extended Hubbard functionals, that are compared with those using local density approximation (LDA), generalized gradient approximation (GGA), and Hybrid (HSE06) functionals. The properties of all three compounds calculated by extended Hubbard functionals are in good agreement with experimental data. We find a substantial increase in band gaps due to the inter-site Coulomb interactions, which show better agreement with $GW$ results compared to those from LDA and GGA functionals. The crucial role of the inter-site Coulomb interactions in restoring the suppressed polar instability, which is computed when only the on-site Hubbard interactions are considered, is also highlighted. Overall, we find that the properties calculated using our extended Hubbard functionals exhibit trends similar to those obtained with the HSE06 functional, while reducing computational costs by over an order of magnitude. Thus, we propose that the current method is well-suited for high-throughput calculations for perovskite oxides, offering significantly improved accuracy in computing band gap and other related physical properties such as the shift current photovoltaic effect and band alignments in ferroelectric heterostructures.

cond-mat.mtrl-sci↗

arXiv2024

A DFT+$U$+$V$ study of pristine and oxygen-deficient HfO$_2$ with self-consistent Hubbard parameters

HfO$_2$-based ferroelectrics have emerged as promising materials for advanced nanoelectronics, with their robust polarization and silicon compatibility making them ideal for high-density, non-volatile memory applications. Oxygen vacancies, particularly in positively charged states, are suggested to profoundly impact the polymorphism kinetics and phase stability of hafnia, thereby affecting its ferroelectric behavior. The electronic structures of pristine and oxygen-deficient hafnia polymorph have been extensively studied using density functional theory, primarily employing (semi-)local exchange-correlation functionals. However, these methods often underestimate band gaps and may not accurately capture the localized nature of $d$-electrons. In this work, we investigate hafnia in various phases using DFT + $U$ + $V$, with onsite $U$ and intersite $V$ Hubbard parameters computed self-consistently via the pseudohybrid Hubbard density functional, ACBN0, and its extended version eACBN0. We find that the self-consistent DFT + $U$ method provides comparable accuracy to the computationally more expensive Heyd-Scuseria-Ernzerhof (HSE) hybrid density functional in predicting relative thermodynamic stability, band gaps, and density of states. Furthermore, it is a cost-effective approach for estimating the formation energies of oxygen vacancies. Additionally, we demonstrate that environmentally dependent Hubbard parameters serve as useful indicators for analyzing bond strengths and electronic structures in real space.

cond-mat.mtrl-sci↗

arXiv2024

Effects of self-consistent extended Hubbard interactions and spin-orbit couplings on energy bands of semiconductors and topological insulators

A first-principles computational method with self-consistent on-site and inter-site Hubbard functionals is able to treat local and non-local Coulomb interactions on an equal footing. To apply the method to understand solids with strong spin-orbit coupling (SOC), we have extended a psuedohybrid functional approach developed by Agapito-Curtarolo-Buongiorno Nardelli to implement self-consistent extended Hubbard energy functionals for noncollinear spin states. With this, energy bands of semiconductors with various SOC strengths such as Si, Ge, GaAs, GaSb, CdSe and PdO are obtained, agreeing with results from fully relativistic $GW$ approximation (FR-GWA) as well as experiments. We also compute energy gaps of HgTe, CuTlS$_2$, and CuTlSe$_2$ and assign them to be topological insulators correctly, unlike characteristic failures for judging topological properties from typical hybrid functionals. We demonstrate feasibility of our method to handle large systems by computing surface bands of topological insulators, Bi$_{\text{2}}$Se$_{\text{3}}$ and Bi$_2$Te$_3$ with varying thickness up to eight quintuple layers. Considering its low computational cost comparable to conventional {\it ab intio} methods and improved accuracy to FR-GWA, we expect that our method provides an opportunity to study large scale correlated systems with the strong SOC efficiently and reliably.

cond-mat.mtrl-sci↗

arXiv2024

Self-consistent tight-binding calculations with extended Hubbard interactions in rhombohedral multilayer graphene

We study the mean-field broken symmetry phases of charge neutral multilayer rhombohedral graphene within tight-binding approximations including self-consistent extended Hubbard interactions. We used on-site and inter-site Hubbard interactions obtained from a newly developed first-principles calculation method. Our calculations for systems up to eight layers give rise to electron-hole asymmetries, band flatness, band gaps, and layer anti-ferromagnetic ground states in keeping with available experiments. By including the intersite Hubbard interactions up to the next-nearest neighboring sites, the band gaps are shown to open when the number of layers is larger than three, while the trilayer system maintains its metallic nature with two low energy density of state peaks near the Fermi energy whose separation increases with the range of inter-site Hubbard parameters. Within our framework, the calculated band gaps reflect mean-field ground states with extended Hubbard interactions, in closer agreement with experimental estimates. The tight-binding formulation further enables efficient treatment of large rhombohedral chiral systems, including twisted multilayer graphene.

cond-mat.mes-hall↗

arXiv2022

Lattice dynamical properties of antiferromagnetic oxides calculated using self-consistent extended Hubbard functional method

We study the lattice dynamics of antiferromagnetic transition-metal oxides by using self-consistent Hubbard functionals. We calculate the ground states of the oxides with the on-site and intersite Hubbard interactions determined self-consistently within the framework of density functional theory. The on-site and intersite Hubbard terms fix the errors associated with the electron self-interaction in the local and semilocal functionals. Inclusion of the intersite Hubbard terms in addition to the on-site Hubbard terms produces accurate phonon dispersion of the transition-metal oxides. Calculated Born effective charges and high-frequency dielectric constants are in good agreement with experiment. Our study provides a computationally inexpensive and accurate set of first-principles calculations for strongly-correlated materials and related phenomena.

cond-mat.str-el↗

arXiv2022

Intersite Coulomb Interactions in Charge Ordered Systems

Using {\it ab initio} approaches for extended Hubbard interactions coupled to phonons, we reveal that the intersite Coulomb interaction plays important roles in determining various distinctive phases of the paradigmatic charge ordered materials of Ba$_{1-x}$K$_x A$O$_3$ ($A=$ Bi and Sb). We demonstrated that all their salient doping dependent experiment features such as breathing instabilities, anomalous phonon dispersions, and transition between charge-density wave and superconducting states can be accounted very well if self-consistently obtained nearest neighbor Hubbard interaction are included, thus establishing a minimal criterion for reliable descriptions of spontaneous charge orders in solids.

cond-mat.str-el↗

arXiv2021

Ab initio study of lattice dynamics of group IV semiconductors using pseudohybrid functionals for extended Hubbard interactions

We study the lattice dynamics of group IV semiconductors using fully ab-initio extended Hubbard functional. The onsite and intersite Hubbard interactions are determined self-consistently with recently developed pseudohybrid functionals and included in force calculations. We analyze the Pulay forces by the choice of atomic orbital projectors and the force contribution of the onsite and intersite Hubbard terms. The phonon dispersions, Gruneisen parameters, and lattice thermal conductivities of diamond, silicon, and germanium, which are most-representative covalent-bonding semiconductors, are calculated and compared with the results using local, semilocal, and hybrid functionals. The extended Hubbard functional produces increased phonon velocities and lifetimes, and thus lattice thermal conductivities compared to local and semilocal functionals, agreeing with experiments very well. Considering that our computational demand is comparable to simple local functionals, this work thus suggests a way to perform high-throughput electronic and structural calculations with a higher accuracy.

cond-mat.mtrl-sci↗