Abstract The simulation of molecular electronic structure on quantum processors is constrained by a spatial mismatch between long-range Coulomb interactions and finite processor connectivity. In this work, we present bounds on the computational resource overhead imposed by the geometric constraint. We show that for molecular systems in the constant-density regime, achieving chemical accuracy requires Hamiltonian nonlocality that scales polynomially with system size and inversely with spatial dimensionality. Due to the finite bisection bandwidths and Lieb–Robinson velocity limits of local processors, this nonlocality imposes a resource cost. Furthermore, we show that in a first-order Trotter–Suzuki-based formulation, the finite duration required to implement non-local Pauli strings amplifies the coherent error accumulation. The geometric constraint requires the non-Clifford gate count to scale quadratically with both the simulation time and the Hamiltonian nonlocality.
Abstract We assess the suitability of the Thomas–Fermi– λ von Weizsäcker (TF λ vW, λ = 0.2 ) functional in orbital-free density functional theory (DFT) for describing itinerant magnetism. We evaluate the magnetic stability through the susceptibility obtained from the second derivative of the total energy with respect to the net magnetization. We perform calculations for the non-ferromagnetic metals Al, Pd, V, Pt, Mo, Ir, and Cr and the canonical ferromagnets Fe, Co, and Ni, benchmarking the results against Kohn–Sham DFT. The TF λ vW results show poor agreement with the Kohn–Sham predictions, failing to correctly identify which systems are ferromagnetic. Using the TF λ vW ground-state density with generalized gradient approximation-level kinetic energy density functionals in a non-self-consistent calculation similarly fails to distinguish ferromagnetic from non-ferromagnetic metals, and yields better agreement with Kohn–Sham benchmarks in some cases and worse in others. Using the TF λ vW ground-state density with the Kohn–Sham functional in a non-self-consistent calculation correctly distinguishes ferromagnetic from non-ferromagnetic metals, although quantitative accuracy remains limited. These results highlight fundamental limitations of the TF λ vW functional for describing itinerant magnetism.
Abstract A solvation model with atom-dependent dielectric constants is developed based on the fragment molecular orbital method interfaced with the polarizable continuum model. Using this method, it is possible to describe heterogeneous solvation, with an interface of media with different dielectric constants. The accuracy of the model is demonstrated for a polypeptide and the method is applied to the hen egg lysozyme protein (1IEE).
Abstract Density functional theory (DFT) is widely used for electronic structure calculations, primarily utilizing the Kohn–Sham scheme. However, this approach reintroduces orbitals, resulting in a high computational cost. In contrast, the original orbital-free Hohenberg–Kohn DFT (OF-DFT) offers the potential for linear-scaling computations suitable for large systems. The advancement of OF-DFT relies on the development of an accurate and universal kinetic energy density functional (KEDF). This review surveys the progress, challenges, and prospects in KEDF development. It presents the essential physical and mathematical constraints that any KEDF must comply with, tracing the evolution from early models like Thomas–Fermi and von Weizsäcker to contemporary semi-local, nonlocal, and machine-learned approaches. While the developed KEDFs have improved the treatment of metals and some semiconductors, achieving transferable accuracy for molecules and systems with considerable density inhomogeneities remains a critical challenge. We highlight two emerging paradigms; the use of physics-guided machine learning to identify accurate KEDFs and information-theoretic approaches that provide deep insights. The path forward requires a renewed focus on fundamental physical constraints, steering the field away from purely empirical fitting toward a universal, computationally efficient KEDF that maximizes the advantages of OF-DFT. The main KEDFs are listed, including gradient expansions, enhancement-factor strategies, density-decomposition methods, and nonlocal KEDFs guided by linear-response theory.
Ga 2 O 3 has garnered substantial interest owing to its promising applications in power electronics and optoelectronics. Herein, the electronic properties of N-doped κ -Ga 2 O 3 are explored through density functional theory calculations. A variety of N-doped complex defects are examined, including N O (N-doped κ -Ga 2 O 3 ), N O V O (N-doped κ -Ga 2 O 3 with O vacancy), N O V Ga (N-doped κ -Ga 2 O 3 with Ga vacancy), N O O i (N-doped κ -Ga 2 O 3 with O interstitial), N O Ga i (N-doped κ -Ga 2 O 3 with Ga interstitial), alongside nitrogen substituting gallium at tetrahedral ( N Ga , tetra ) and octahedral ( N Ga , octa ) sites. Analysis of their formation energies reveals that N O predominates under both Ga-rich and O-rich environments, functioning as a shallow acceptor. Intriguingly, under Ga-rich conditions, there exists a pronounced preference for N O V O defects over other acceptor-like deep defects, implying that such complexes may obstruct the attainment of p-type conductivity in κ -Ga 2 O 3 due to extensive compensation by oxygen vacancies. Moreover, it is demonstrated that N O V O complexes can elicit red luminescence, arising from oxygen vacancies coupled with holes localized at acceptor sites introduced by N doping. The intricate electronic structure of κ -Ga 2 O 3 with these complex defects is elucidated through comprehensive analyses of the density of states and electronic band structures. Complementary examinations of electron localization and real-space wavefunctions further illuminate the influence of these defects on the κ -Ga 2 O 3 lattice. Notably, N-doped κ -Ga 2 O 3 exhibits enhanced anion diffusion and charge delocalization, suggesting that nitrogen doping can substantially improve hole mobility and electrical conductivity. This study offers valuable theoretical insights into the limitations and prospects of nitrogen doping as a method for achieving p-type conductivity in κ -Ga 2 O 3 .
The advent of computational and experimental approaches of novel two-dimensional (2D) metal carbides and nitrides, encompassing a variety of metal species of group IIA, IIB, IIIA and various transition metals (collectively known as MXenes) has unveiled significant advances in materials science and technology. Among them, alkaline-earth metal nitrides and carbides (AEXenes) have attracted enormous attention particularly following the experimental realization of few AEXenes as a 2D electride. Herein we have systematically reviewed the structural, electronic, thermal, mechanical, magnetic and optical properties of the 2D AEXenes, reported in recent literature. Leveraging these intriguing features, we have assigned their prospective applications across diverse domains including energy storage, energy harvesting, catalytic and spintronic devices. For instance, BeN monolayers possess significantly high storage capacity (3489 mAh gm −1 ) with low diffusion barrier and placing them on par with functionalized MXenes. However, Mg 2 C and Mg 3 C 2 display remarkably low lattice thermal conductivity of 20.26 Wm −1 K −1 and 1.5 Wm −1 K −1 , attributed to distinctive structural complexity, elevated scattering rate and ultimately result better energy conversion efficiency. We have further outlined viable approaches i.e. external carrier doping, adsorption, various defect engineering to modulate their electronic and magnetic properties to facilitate themselves for different applications. In this topical review, we aim to explore recent advancement of these functionalized materials and their isoelectronic analogues to harness their exceptional properties from both theoretical and experimental perspectives.
Abstract Electronic-structure theory is the foundation of the description of materials including multiscale modeling of their properties and functions. Obviously, without sufficient accuracy at the base, reliable predictions are unlikely at any level that follows. The software package FHI-aims has proven to be a game changer for accurate free-energy calculations because of its scalability, numerical precision, and its efficient handling of density functional theory (DFT) with hybrid functionals and van der Waals interactions. It treats molecules, clusters, and extended systems (solids and liquids) on an equal footing. Besides DFT, FHI-aims also includes quantum-chemistry methods, descriptions for excited states and vibrations, and calculations of various types of transport. Recent advancements address the integration of FHI-aims into an increasing number of workflows and various artificial intelligence (AI) methods. This Roadmap describes the state-of-the-art of FHI-aims and advancements that are currently ongoing or planned.
Transition-metal nanoclusters are of primary interest in catalysis. In addition to conventional experimental techniques, these molecules are studied computationally to unravel their structural, energetic, and mechanistic properties. However, almost all studies in the literature neglect relativistic effects, which, for sixth-period metals, affect the accuracy of the results. In this study, we investigate the structural and electronic properties of the Ir4(CO)12 cluster and its bare tetrahedral precursor Ir4, using nonrelativistic and relativistic computational methods, including DFT and CCSD(T). The comparison of the results obtained demonstrates that the theoretical study of nanoclusters of this type must be conducted using a methodological approach that necessarily incorporates relativistic corrections to ensure reliable, accurate output. Furthermore, our findings suggest that computational studies on nanoclusters containing iridium atoms in the literature need to be critically revisited.
Assessing the dynamical stability of computationally predicted metal–organic frameworks (MOFs) is essential to distinguish synthetically feasible structures from dynamically unstable ones. However, reliable first-principles phonon calculations on these systems remain challenging: their large, flexible unit cells and soft collective modes make the vibrational spectrum highly sensitive to the numerical settings. Using MOF-5 as a representative case study, we establish a finite-displacement workflow to identify and isolate the origins of imaginary phonon modes. We demonstrate how numerical force convergence thresholds, real-space grid resolutions, symmetry-standardization protocols, and alternative unit-cell representations can qualitatively and spuriously alter the predicted lattice stability. Once numerical noise is confidently excluded, the remaining imaginary modes can be analyzed through mode mapping or stochastic Monte Carlo symmetry-breaking distortions to locate lower-energy local minima. This protocol provides a robust, transferable strategy for the reliable assessment of dynamical stability and lattice vibrations in flexible porous frameworks.
The accurate identification of static (non-dynamical) electron correlation remains a fundamental challenge in quantum chemistry, particularly for systems that exhibit pronounced multireference (MR) character. In this work, we derive two diagnostics, RMAX and Delta epsilon MAX, for quantifying the MR nature of molecular systems. Both indices are rigorously derived from the Grand Potential of Fermions (GPFs) and are dependent on natural orbitals, offering complementary perspectives on the degree of static correlation in electronic species. Univocal numerical thresholds are provided to identify cases where static correlation significantly impacts the electronic structure. An evaluation was also performed using two well-established diagnostics, INDMAX and D2[MP2], as benchmarks. Our results reveal excellent agreement between the proposed and reference diagnostics, with Pearson correlation coefficients exceeding 0.93 across a customized dataset of 1925 chemical systems, extracted from the GMTKN55 database. The strong correspondence between RMAX, Delta epsilon MAX and INDMAX, D2[MP2] confirms that the GPFs provides a physically meaningful and transferable foundation for diagnosing MR character. Their balance of interpretability, computational efficiency, and diagnostic accuracy makes them promising tools for guiding the selection of electronic structure methods and identifying cases where single-reference approaches may be insufficient.
Carbon clusters are fundamental building blocks of nanostructured carbon materials with applications in materials science, biomaterials, and energy technologies. In this work, the structural stability, electronic properties, and vibrational characteristics of small carbon clusters Cn (n = 3-8) were investigated using ab initio methods, including Hartree-Fock (HF), density functional theory (DFT) with the B3LYP functional with and without Grimme's dispersion correction, and coupled-cluster singles and doubles (CCSD). Calculations employed the 6-31+G(d), 6-311+G(d,p), and cc-pVTZ basis sets. Linear isomers were identified as the most stable structures for all cluster sizes, indicating that linear geometries can already be captured at the HF level. Binding energies increase with cluster size, while DFT and CCSD accurately reproduce stability trends and identify C3 and C5 as magic-number clusters. Vibrational analyses reveal dominant asymmetric stretching modes in the mid-infrared (IR) region and bending modes in the far-IR region, consistent with available experimental data.
We present the modification of electronic structure properties due to the presence of oxygen vacancies in monoclinic-zirconia (m-ZrO2). Using a combined density functional theory (DFT) and GW formalism, we study the electronic structure and charge transition levels (CTLs) of oxygen vacancy (OV) defects in m-ZrO2. The CTLs are calculated using two paths and employing electrostatic corrections due to localized charge at the defect site. We find +1/0 CTL is at 3.48 eV (2.50 eV) and +2/+1 CTL is at 1.92 eV (0.98 eV) for 3-fold (4-fold) OV in m-ZrO2. We also describe a relaxation mechanism of atoms near an OV site. Finally, we compare the calculated CTLs using only DFT and the combined approach of both DFT and GW method with appropriate electrostatic corrections. Our results agree well with the experimental findings of electronic trap level in m- ZrO2, as reported by Mondal et al (2020 IEEE Electron. Dev. Lett. 41 717-20), Li et al (2010 Thin Solid Films 518 6382-4), Cong et al (2009 J. Phys. Chem. C 113 13974-8)
A systematic first-principles investigation of the structural, electronic, vibrational, and mechanical properties of Ag7PS6 is presented. The effects of different exchange-correlation functionals and Grimme dispersion corrections on the optimized unit-cell parameters are quantitatively analyzed. It is demonstrated that the inclusion of dispersion interactions leads to improved agreement with experimental lattice constants and interatomic distances. The phonon dispersion and partial phonon density of states confirm the dynamical stability of the optimized structure, with no imaginary modes observed. The calculated vibrational spectra show good agreement with Raman measurements. Furthermore, the elastic constants and derived mechanical parameters, including the B/G ratio, indicate a ductile mechanical behavior of Ag7PS6.
Ga2O3 has garnered substantial interest owing to its promising applications in power electronics and optoelectronics. Herein, the electronic properties of N-doped kappa-Ga2O3 are explored through density functional theory calculations. A variety of N-doped complex defects are examined, including NO (N-doped kappa-Ga2O3), NOVO (N-doped kappa-Ga2O3 with O vacancy), NOVGa (N-doped kappa-Ga2O3 with Ga vacancy), NOOi (N-doped kappa-Ga2O3 with O interstitial), NOGai (N-doped kappa-Ga2O3 with Ga interstitial), alongside nitrogen substituting gallium at tetrahedral ( NGa,tetra) and octahedral ( NGa,octa) sites. Analysis of their formation energies reveals that NO predominates under both Ga-rich and O-rich environments, functioning as a shallow acceptor. Intriguingly, under Ga-rich conditions, there exists a pronounced preference for NOVO defects over other acceptor-like deep defects, implying that such complexes may obstruct the attainment of p-type conductivity in kappa-Ga2O3 due to extensive compensation by oxygen vacancies. Moreover, it is demonstrated that NOVO complexes can elicit red luminescence, arising from oxygen vacancies coupled with holes localized at acceptor sites introduced by N doping. The intricate electronic structure of kappa-Ga2O3 with these complex defects is elucidated through comprehensive analyses of the density of states and electronic band structures. Complementary examinations of electron localization and real-space wavefunctions further illuminate the influence of these defects on the kappa-Ga2O3 lattice. Notably, N-doped kappa-Ga2O3 exhibits enhanced anion diffusion and charge delocalization, suggesting that nitrogen doping can substantially improve hole mobility and electrical conductivity. This study offers valuable theoretical insights into the limitations and prospects of nitrogen doping as a method for achieving p-type conductivity in kappa-Ga2O3.
This study presents a comprehensive density functional theory analysis of the structural and electronic modifications induced by point defects and spin-orbit coupling in monolayer 1H-WSe2. Among intrinsic point defects, the selenium vacancy is identified as the most energetically favorable and is shown to generate well-localized in-gap states predominantly originating from the d orbitals of neighboring W atoms. Spin-orbit coupling lifts the spin degeneracy of these defect states, giving rise to pronounced spin splitting with a dominant out-of-plane spin component as a consequence of broken local in-plane mirror symmetry and the strong atomic spin-orbit interaction of tungsten. Spin-resolved band structure calculations further reveal valley-dependent spin polarization with a dominant out-of-plane spin component at the K and K ' points, indicating a nontrivial coupling between defect states and the spin and valley degrees of freedom. The essential features of the defect-induced spin splitting and spin texture are captured by a minimal k & sdot;p Hamiltonian, providing analytical insight into the underlying symmetry and spin-orbit mechanisms. Our results establish defect engineering as an effective route to realize localized spin-polarized states in two-dimensional transition metal dichalcogenides, offering promising prospects for spintronic and valleytronic quantum device applications.
In this work, we present a fragment-based divide-and-conquer (FDC) method. The proposed FDC method is an efficient linear-scaling algorithm based on non-orthogonal localized molecular orbitals (NOLMOs). In the NOLMO-FDC method, the self-consistent field (SCF) procedure is performed only for subsystems, eliminating the need to carry out an SCF calculation for the entire system. This significantly reduces the computational cost associated with repeatedly constructing the full-system Fock matrix. At the same time, the NOLMO-FDC method maintains an accuracy comparable to that of our previously proposed NOLMO-DC method. To mitigate environmental truncation effects-particularly in strongly polar systems-an external point-charge model is introduced to ensure electrostatic consistency across fragment boundaries. The method is tested on polyacetylene, water clusters, and peptide chains. Compared with the conventional DC method, the NOLMO-FDC approach improves accuracy by approximately 1.5 to 2 orders of magnitude. It also achieves up to a tenfold speedup over Hartree-Fock and a two- to threefold improvement in efficiency relative to NOLMO-DC. The high accuracy and efficiency of the NOLMO-FDC method make it well suited for electronic-structure studies of large systems.
The ability to engineer molecular junctions with tunable spin and thermoelectric properties is central to the development of high-performance nanoscale devices. In this work, we investigate endohedral fullerenes M@C80 (M=Fe, Co, Ni) contacted by gold and graphene electrodes using density functional theory combined with the non-equilibrium Green's function formalism. Encapsulation of transition-metal atoms inside the C-80 cage induces pronounced charge transfer, orbital hybridization, and spin splitting, leading to strongly modulated and energy-selective transmission spectra. The Au-Fe@C-80-Au junction exhibits the highest spin polarization and near-unity transmission at the Fermi level, making it particularly suitable for spintronic applications. In contrast, the Gr-Co@C-80-Gr junction displays an exceptionally large thermoelectric response. The thermoelectric figure of merit is reaching ZT > 1000 which originates from sharp, asymmetric transmission resonances near the Fermi energy and enhanced pi-pi coupling with graphene. These values represent upper theoretical limits within a coherent electronic transport regime and do not imply a violation of thermodynamic constraints, as the thermoelectric efficiency remains bounded by the Carnot limit. The Ni@C-80 junction shows broader transmission features, which are favorable for energy-selective transport. A comparative analysis of electrode materials reveals that gold provides stronger and more stable molecule-electrode coupling with higher electrical conductance, whereas graphene enables superior energy filtering and an enhanced Seebeck response.
We investigate the pressure-induced spin crossover in ferropericlase (Mg 1-xFexO, x=0.03125-0.25) using first-principles calculations with generalized gradient approximation (GGA + U) and HSE06 methods. By analyzing spin transition pressures, structural distortions, and electronic properties, we establish a correspondence between the Hubbard U and hybrid mixing parameter alpha. Both methods predict a linear increase in transition pressure with Fe concentration and show weak sensitivity to Fe distribution. Our findings clarify the strengths and limitations of each approach and provide guidance for modeling spin transitions in mantle materials.
The platinum oxide Pt3O4 exhibits metallic conductivity even though it contains square-planar PtO4 units, which in related oxides such as PtO are usually associated with insulating behavior. To identify the electronic origin of this anomalous metallicity, we performed a comprehensive first-principles study using the PBE and r(2)SCAN functionals together with Hubbard U corrections and spin-orbit coupling (SOC). Structural benchmarks show that r(2)SCAN with SOC and a moderate U value ( similar to 4eV) reproduces the experimental lattice constants and formation enthalpy, whereas larger U values (similar to 8eVeV) destabilize the cubic structure. Across all functionals and U values considered in this work, Pt3O4 remains metallic. Analyses of the projected density of states, band structures, charge-density isosurfaces, and bonding characteristics demonstrate that the dominant contribution to the metallic character originates from delocalized Pt-O-Pt hybridized antibonding states at the Fermi level. Direct Pt-Pt interactions are present but contribute less strongly to the conductivity. Bader charge analysis reveals only weak Pt charge disproportionation, consistent with mixed Pt-II/Pt-III character, and a small charge-transfer energy that prevents localization of the Pt 5d electrons even at elevated U. In contrast, PtO develops a Mott or charge-transfer gap under modest U despite having the same PtO4 coordination environment. These findings demonstrate that persistent Pt-O-Pt covalency is the primary driver of metallicity in Pt3O4 and support the view that this phase can remain conductive under oxygen reduction and oxygen evolution reaction conditions in fuel cell and electrolyzer environments.
