Accurately predicting excited-state properties of heterogeneous systems remains a central challenge in computational chemistry and materials science. Dielectric-dependent hybrid functionals have achieved notable success for bulk semiconductors and insulators, but their reliance on a scalar macroscopic dielectric constant hampers their applicability to systems with spatially inhomogeneous screening environments. Here, we use hybrid functionals with spatially dependent screened exchange within linear-response time-dependent density functional theory (TDDFT), and we evaluate analytical excited-state forces, enabling geometry relaxation on excited-state potential-energy surfaces and the computation of adiabatic excitation energies. We first consider point defects in three-dimensional bulk hosts, including diamond, silicon carbide, and magnesium oxide, and we show that our approach preserves the accuracy of conventional dielectric-dependent hybrid functionals. For systems with strongly heterogeneous dielectric environments, including the Cr(o-tolyl)4 molecular qubit embedded in a Sn(o-tolyl)4 host matrix and the CBCN defect in monolayer h-BN, hybrid functionals with spatially dependent screened exchange yield substantially improved agreement with experiment and high-level many-body benchmarks, compared to conventional dielectric-dependent hybrid functionals. Our results establish hybrid-functional TDDFT with spatially dependent screened exchange as a broadly applicable and physically motivated strategy for excited-state simulations of complex, inhomogeneous environments.
Jiawei Zhan, Giulia Galli· Journal of Chemical Theory a...· 2 citations
We present WEST, an open-source plane-wave pseudopotential code for large-scale excited-state materials simulations, and describe its theoretical foundations, software architecture, and capabilities. WEST implements full-frequency GW, quantum defect embedding theory, the Bethe-Salpeter equation, and time-dependent density functional theory within a common algorithmic framework that avoids the explicit computation of virtual electronic states. By combining density functional and density matrix perturbation theory, low-rank representations of the dielectric screening and exact exchange, and localization techniques, WEST achieves favorable computational scaling with system size. The code supports the calculation of quasi-particle and neutral excitation energies, optical and photoluminescence spectra, excited-state forces, and non-adiabatic couplings, with interoperable workflows connecting to quantum chemistry, vibronic coupling, and quantum computing packages. A hierarchical parallelization strategy and GPU acceleration deliver near-ideal strong scaling to thousands of GPUs, enabling accurate excited-state simulations of systems with more than a thousand atoms. Representative applications, spanning the full optical cycle of solid-state spin defects, self-trapped excitons in metal-halide perovskites, and the optical response of liquid water and ice, demonstrate the accuracy and versatility of the code across diverse material classes. The capabilities implemented in WEST establish the code as a scalable platform for predictive excited-state simulations, high-throughput materials discovery, and the generation of high-fidelity datasets for machine learning in computational materials science.
V. Yu, Siyuan Chen, Yu-Ming Jin et al.· 2 citations
We present an efficient plane-wave implementation of analytical nuclear forces for electronic excited states described by the Bethe-Salpeter equation (BSE). The formulation combines density-matrix perturbation theory with a Lagrangian approach, and avoids both explicit empty-state summations and the response calculations for each atomic displacement, required by conventional approaches based on density functional perturbation theory. Together with GPU acceleration, these advances make BSE forces calculations tractable for solid-state systems containing hundreds of atoms. We demonstrate the method on two point defects with distinct dielectric environments: the nitrogen-vacancy center in diamond, where BSE and time-dependent density functional theory (TDDFT) yield consistent excited-state relaxations, and the carbon-dimer defect in two-dimensional hexagonal boron nitride, where the screened electron-hole interaction included in the BSE stabilizes the localized defect excitation and corrects the relaxation pattern predicted by semilocal TDDFT. These results establish a scalable framework for BSE-level studies of excited-state relaxation and vibronic coupling in heterogeneous condensed systems.
Yu-Ming Jin, V. Yu, M. Govoni et al.· 2 citations· ⚡1
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