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.
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 first-principles approach for simulating the nonequilibrium electron dynamics in extended systems beyond the linear regime. The method combines Koopmans-compliant functionals, which provide an accurate quasiparticle band structures, with the real-time evolution of the electronic density matrix in a Wannier basis within the Hartree plus screened exchange (HSEX) approximation. The locality of the orbital basis enables physically motivated approximations that significantly reduce both the computational cost and memory requirements while preserving accuracy. The screened Coulomb interaction, the central ingredient of the HSEX self-energy, is computed efficiently using density-functional perturbation theory. We benchmark the approach in the linear regime against experimental spectra and reference Green's function calculations for systems featuring both weakly and strongly bound excitons. Moving to the nonlinear regime, we investigate high-harmonic generation (HHG) in silicon and lithium fluoride. While in silicon the HHG spectrum is largely governed by the quasiparticle band structure, in LiF, a material featuring strong excitonics effect, the harmonic emission is selectively enhanced at excitonic resonances, suggesting that HHG probes correlated electron-hole excitations rather than solely the quasiparticle band structure. The present framework enables fully \textit{ab-initio} simulations of excitonic effects in nonlinear optical spectra at a significantly reduced computational cost compared to real-time Green's function approaches, providing an efficient route to the study of ultrafast and strong-field phenomena in solids.
G. Cistaro, Miguel S'a, D. Sangalli et al.· 0 citations
We investigate the bound state properties of the hydrogen-like atoms in the radial screened Coulomb potential (RSCP). using three complementary analytical approaches - expectation values with Coulomb and Kratzer reference states, variational optimization with a scaled Kratzer basis, and the Hellmann-Feynman theorem - we derive approximate energy eigenvalues as function of the screening parameter c. Benchmarked against high-precision generalized pseudospectral data, the expectation value-approach with the Kratzer basis achieves relative errors of 0.63% for the first ten s-states at $c=0.1$, while the variational method improves this further. The formalism extends naturally to Positronium, demonstrating its generality for arbitrary reduced-mass systems. The complementary biases of the methods provide robust error estimation for plasma-embedded atoms.
Fatma-Zohra Khaled, Mustafa Moumni, M. Falek· 0 citations
The electron self-energy is central to quasiparticle theory, yet how an optical cavity enters it remains unclear. We address this question for a molecule in a single-mode cavity using the dipole-gauge Pauli-Fierz Hamiltonian and a coherent-state QED Hartree-Fock reference. The cavity enters through three channels: the static dipole self-energy (DSE) shift of reference orbital energies, direct DSE augmentation of the screened interaction, and the polariton pole carrying the bilinear electron-photon coupling. We benchmark QED-$GW$ ionization potentials (IPs) and electron affinities (EAs) against a cavity $\Delta$-method ladder from QED-HF to correlated wave-function methods, whose cavity-induced shifts agree within 1 meV where directly comparable. For closed-shell molecules with unbound anions, $GW$ systematically overestimates cavity-induced IP redshifts, whereas EA shifts are reproduced nearly quantitatively, although this does not imply comparable accuracy for absolute EAs. For ionic molecules with bound anions, this ordering reverses, consistent with published QED coupled-cluster results. Coupling and detuning scans show that the error is predominantly quadratic in $\lambda$ and DSE-driven rather than resonant. The spectral function develops a polariton-replica photoemission sideband with weight scaling as $\lambda^2$. In the static screened interaction used in the Bethe-Salpeter equation, bare-photon exchange cancels the matching DSE contribution to the direct interaction, while exchange and polariton-screening corrections remain. Their net effect on the lowest excitation is appreciable only for ammonia in the molecules studied. Exciton-binding energies involving unbound anions are strongly basis-dependent and should therefore be viewed as diagnostics of electron-hole interactions rather than basis-converged molecular quantities.
S. Yoo, G. Willow, Tae Beom Sim et al.· 0 citations
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 a refined strong-field approximation (SFA) theory incorporating the intermediate-state Coulomb interaction for nonsequential double ionization (NSDI). By introducing the Coulomb−Volkov wave function into the intense-field many-body S-matrix theory, we develop an intermediate-state Coulomb-corrected strong-field approximation (ICSFA) to address the long-standing deficiency of neglecting the Coulomb potential acting on the recolliding electron. Using the recollision excitation with subsequent ionization (RESI) mechanism in helium as a benchmark, we perform a systematic comparison between the conventional SFA and the ICSFA. The correlated electron momentum distributions (CEMDs) calculated via ICSFA show a significant redistribution of electron yield toward high-momentum regions and off-axis quadrants, which aligns quantitatively with experimental observations, whereas the SFA fails to reproduce these features. Concurrently, the joint energy distributions (JEDs) manifest a corresponding evolution. Analysis reveals that the Coulomb potential promotes large-angle scattering, thereby reshaping the CEMD and the JED. Furthermore, the ICSFA reveals a substantial enhancement of multiple-return recollision (MRR) trajectories, stemming from the combined effects of Coulomb focusing (manifested through the normalization factor) and the energy-dependent enhancement of the inelastic scattering cross-section. Our work establishes that the intermediate-state Coulomb interaction is indispensable for a quantitatively accurate description of strong-field correlated electron dynamics.
Chunli Miao, Hao Ren, Chan Li et al.· Chinese Physics Letters· 0 citations
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