arXiv subjects

Feliciano Giustino

Publications and source records attributed to Feliciano Giustino.

At least 19 recordsLinked to original sources

arXiv2026

Polarons from first principles

This article reviews recent theoretical developments in the ab initio study of polarons in materials. The polaron is an emergent quasiparticle that arises from the interaction between electrons and phonons in solids, and consists of an electron or a hole accompanied by a distortion of the crystal lattice. Recent advances in experiments, theory, and computation have made it possible to investigate these quasiparticles with unprecedented detail, reigniting the interest in this classic problem of condensed matter physics. Recent theoretical and computational advances include ab initio calculations of polaron spectral functions, wavefunctions, lattice distortions, and transport and optical properties. These developments provide new insight into polaron physics, but they have evolved somewhat independently from the earlier effective Hamiltonian approaches that laid the foundation of the field. This article aims to bridge these complementary perspectives by placing them within a single unified conceptual framework. To this end, we start by reviewing effective Hamiltonians of historical significance in polaron theory, ab initio techniques based on density functional theory, and many-body first-principles approaches to polarons. After this survey, we outline a general field-theoretic framework that bridges between these diverse approaches to polaron physics. For completeness, we also review recent progress in the study of exciton polarons and self-trapped excitons and their relations to polarons. Beyond the methodology, we discuss recent applications to several classes of materials that attracted attention in the context of polaron physics.

cond-mat.mtrl-sci↗

arXiv2026

Nonlinear electron-phonon interactions from first principles

Electron-phonon interactions underpin a variety of phenomena, ranging from transport and superconductivity to polarons and ultrafast carrier dynamics. Despite being one of the most intensely studied subjects in condensed matter physics, research on electron-phonon physics mostly focused on linear, first-order couplings. Second- and higher-order nonlinear couplings are commonly ignored because their calculations are too demanding and we lack computational frameworks that can provide both diagonal and off-diagonal coupling matrix elements. In this work, we report a theory and computational method for computing nonlinear electron-phonon interactions of any order in real materials. Our approach combines the advantages of unit-cell calculations of electron wavefunctions and supercell calculations of phonon perturbations, is systematically improvable, can be used with either semilocal or nonlocal exchange-correlation functionals, and is amenable to Wannier-Fourier interpolation. As a first proof of concept, we illustrate this method by computing second-order electron-phonon coupling matrix elements in diamond, lithium fluoride, and graphite as representative nonpolar semiconductors, polar semiconductors, and metals, respectively. Furthermore, we generalize the ab initio polaron equations to second-order electron-phonon couplings, and we show that second-order couplings are essential to achieve quantitative accuracy in polaron formation energies and hopping barriers. The present methodology will find application in the study of all properties and phenomena that are currently being investigated within the linear electron-phonon coupling approximation, from phonon-mediated superconductivity to excited-states dynamics, both in harmonic and anharmonic systems.

cond-mat.mtrl-sci↗

arXiv2026

Electron correlation in semiconductors and insulators via symbolic regression

Predicting quasiparticle energies in materials requires expensive numerical evaluations of the electron self-energy. This limits calculations to ordered systems with small unit cells. Here, using symbolic regression, we show that the GW self-energy can be accurately approximated with compact analytical functions of physically motivated Kohn-Sham descriptors. These expressions can be learned from a single GW calculation in the ordered phase and remain accurate under symmetry breaking induced by quantum and thermal fluctuations, elastic deformations, and amorphous disorder. This development enables routine GW calculations of complex materials with thousands of atoms at a computational cost comparable to semi-local density functional theory. We demonstrate the accuracy of this approach for covalent semiconductors, ionic insulators, and two-dimensional materials. These results establish symbolic regression as a viable route to predictive, interpretable, and transferable many-body electronic structure models.

cond-mat.mtrl-sci↗

arXiv2026

Balanced electron and phonon heat transport in metallic $\varepsilon$-TaN

Most materials with high thermal conductivity belong to one of two classes: metals, where heat is carried predominantly by electrons, and insulators, where heat transport is dominated by the phonon contribution. Materials that combine substantial electronic thermal conductivity and lattice thermal conductivity are rare, because the mechanisms that favor electron transport typically suppress phonon transport, and vice versa. Here, we report the theoretical prediction and experimental realization of such a material, metallic $\varepsilon$-TaN. Our calculations predict a total thermal conductivity at room-temperature of 273$\pm$5Wm$^{-1}$K$^{-1}$ in single crystals and 145$\pm$5Wm$^{-1}$K$^{-1}$ in polycrystals with 0.5$μ$m grains, with an unusually large lattice contribution (79%) for a metal. The latter value is in agreement with our local transient thermoreflectance measurements on polycrystalline samples yielding $\sim$130Wm$^{-1}$K$^{-1}$. We show that the balanced electronic and lattice thermal conductivities of $\varepsilon$-TaN originate from a combination of large Fermi velocity and small Fermi density of states on the electron side, and large speed of sound and wide phonon gap on the lattice side.

cond-mat.mtrl-sci↗

arXiv2026

First-principles predictions of carrier mobility with record accuracy using GW perturbation theory

Accurate prediction of carrier mobility is critical for the discovery and design of next-generation electronic materials. Despite sustained progress, state-of-the-art ab initio methods remain limited by the approximate treatment of electron-phonon interactions at the density functional theory level. Here, we demonstrate that incorporating many-body GW corrections to both the electronic band structure and electron--phonon couplings when solving the ab initio Boltzmann transport equation yields a mean absolute relative error of just 11% for electron mobilities across benchmark semiconductors, including Si, GaAs, GaP, diamond, and SiC. The common practice of neglecting GW corrections to the electron--phonon interaction can lead to mobility errors exceeding 50%. The present findings highlight the importance of many-body GW self-energy effects in carrier transport simulations, and provides fundamental insights into how many-body electron--phonon interactions govern charge transport in crystalline solids.

cond-mat.mtrl-sci↗

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

Collective quantum state at the atomic limit

Collective quantum states are often associated with extended systems, where spatially extensive degrees of freedom enable emergent many-body behavior; whether such strongly correlated states survive at atomic dimensions remains a fundamental question. Tomonaga-Luttinger liquids provide a paradigmatic example of one-dimensional collective quantum matter characterized by spin-charge separation. Using low-temperature scanning tunneling microscopy and spectroscopy, we directly visualize quantized collective modes in atomically confined mirror twin boundary segments of monolayer WSe2. Distinct standing-wave branches associated with fractionalized spin and charge excitations persist in segments as short as one nanometer, establishing the atomic-scale confinement limit of Luttinger-liquid behavior. These ultrashort segments form a new class of many-body quantum dots whose discrete spectra arise from confined collective bosonic modes rather than single-particle electron states. When assembled into ordered chains, inter-dot coupling reshapes electron-like fundamental states while collective spin/charge excitations remain largely intact, revealing distinct coupling responses of emergent many-body modes. Our results demonstrate that collective quantum matter can persist and exhibit fundamentally distinct coupling behavior at atomic length scales, establishing a novel platform for engineering strongly correlated quantum phases from atomically confined building blocks.

cond-mat.mes-hall↗

arXiv2026

Meta-optimization of maximally-localized Wannier functions

Maximally-localized Wannier functions are quantum wavefunctions resembling atomic orbitals that are used to describe electrons in condensed matter. Since their introduction in 1997, these functions have become ubiquitous in ab initio materials simulations, including applications in linear-scaling methods, strongly-correlated electron systems, quantum transport, electron-phonon interactions, and topological materials. Despite their widespread adoption in a vast software ecosystem, Wannier functions have not yet attained their fullest potential in the presence of entangled bands, as their optimization remains challenging and labor-intensive. Here, we introduce a universal meta-optimization method that leverages workflow abstraction and machine learning techniques like differential evolution and Bayesian optimization to generate globally optimized Wannier functions without human intervention. We demonstrate this approach through three applications: (i) autonomous interpolation of entangled band structures with millielectronvolt accuracy starting from coarse Brillouin zone grids, (ii) thousand-fold acceleration of fully ab initio Boltzmann transport calculations via the use of minimal coarse Brillouin zone grids, and (iii) ultra-fast high-throughput calculations of high-precision Wannier functions for large materials libraries. This work brings calculations that previously required supercomputers within the reach of personal computers.

physics.comp-ph↗

arXiv2026

Electron-phonon physics at the exascale: A hybrid MPI-GPU-OpenMP framework for scalable Wannier interpolation

We demonstrate a highly efficient GPU implementation of the Wannier interpolation of electron-phonon matrix elements in the EPW code. Building on a systematic analysis of the computational complexity of the algorithm for electron-phonon interpolation, we designed a GPU porting strategy that integrates naturally into the current EPW implementation, and is seamlessly portable to NVIDIA, AMD, and Intel GPUs. We demonstrate this development via extensive benchmarks on conventional semiconductors such as silicon and monolayer MoS$_2$, as well as a large-scale application to topological stanene nanoribbons of width as large as 20nm, which was intractable with previous implementations. Compared to the single MPI parallelization scheme of EPW v5.9, the resulting hybrid MPI-GPU-OpenMP scheme achieves up to 29-fold speedup on leadership-class supercomputers equipped with NVIDIA and Intel accelerators, namely Vista at the Texas Advanced Computing Center, Perlmutter at the National Energy Research Scientific Computing Center, and Aurora at the Argonne Leadership Computing Facility. This framework also achieves nearly ideal scalability up to thousands of GPU nodes on the Aurora supercomputer. With this development, EPW is ready to support electron-phonon physics calculations on exascale platforms.

cond-mat.mtrl-sci↗

arXiv2026

Roadmap for electronic structure, anharmonicity, and electron-phonon calculations in locally disordered inorganic and hybrid halide perovskites

The role of data in modern materials science becomes more valuable and accurate when effects such as electron-phonon coupling and anharmonicity are included, providing a more realistic representation of finite-temperature material behavior. Furthermore, positional polymorphism, characterized by correlated local atomic disorder usually not reported by standard diffraction techniques, is a critical yet underexplored factor in understanding the electronic structure and transport properties of energy-efficient materials, like halide perovskites. In this manuscript, we present a first-principles methodology for locally disordered (polymorphous) cubic inorganic and hybrid halide perovskites, rooted in the special displacement method, that offers a systematic and alternative approach to molecular dynamics for exploring finite-temperature properties. By enabling a unified and efficient treatment of anharmonic lattice dynamics, electron-phonon coupling, and positional polymorphism, our approach generates essential data to predict temperature-dependent phonon properties, free energies, band gaps, and effective masses. Designed with a high-throughput spirit, this framework has been applied across a range of inorganic and hybrid halide perovskites: CsPbI3, CsPbBr3, CsSnI3, CsPbCl3, MAPbI3, MAPbBr3, MASnI3, MAPbCl3, FAPbI3, FAPbBr3, FASnI3, and FAPbCl3. We provide a comprehensive comparison between theoretical and experimental results and we systematically uncover trends and insights into their electronic and thermal behavior. For all compounds, we demonstrate strong and consistent correlations between local structural disorder, band gap openings, and effective mass enhancements.

cond-mat.mtrl-sci↗

arXiv2026

Electron-phonon couplings in polymorphous crystals

Positional polymorphism in solids refers to locally disordered unit cells that, on average, reproduce the high-symmetry structures observed in diffraction experiments. Standard theories of electron-phonon interactions fail to describe the temperature-dependent electronic structure of such polymorphous systems. Hybrid halide perovskites are a prime example, where configurational entropy from both polymorphism and molecular disorder plays a central role. Here we generalize the special displacement method to polymorphous crystals, providing an efficient ab initio framework for electron-phonon couplings without resorting to molecular dynamics. We resolve long-standing discrepancies in hybrid halide perovskite physics, including temperature-dependent anharmonic phonons and band gaps. Our approach provides a practical route to link local disorder, configurational entropy, and electron-phonon interactions, with applicability across diverse material classes, from optoelectronics and ferroelectrics to thermoelectrics.

cond-mat.mtrl-sci↗

arXiv2026

Watching Polarons Form in Real Time

Polaron formation in pump-probe experiments is an inherently non-equilibrium phenomenon, driven by the ultrafast coupled dynamics of electrons and phonons, and culminating in the emergence of a localized quasiparticle state. In this work, we present a first-principles quantum-kinetic theory of polaron formation that captures the real-time evolution of electronic and lattice degrees of freedom in presence of electron-phonon coupling. We implement this framework to investigate the ultrafast polaron formation in the prototypical polar insulator MgO. This approach allows us to determine the characteristic timescales of polaron localization and to identify its distinctive dynamical fingerprint. Our results establish clear and experimentally accessible criteria for identifying polaron formation in pump-probe experiments.

cond-mat.mtrl-sci↗

arXiv2026

Symmetry-protected topological polarons

Emergent quasiparticles in solids often exhibit unique topological properties as a result of the complex interplay between charge, orbital, spin and lattice degrees of freedom. Among these quasiparticles, the polaron occupies a special place as the first known manifestation of the interaction between a fermion and a boson field. While polarons have been investigated for almost a century, whether these quasiparticles exhibit topological properties and why remain open questions. Here, we establish the universal symmetry principles governing the topology of polar textures in large polarons. Using a group-theoretic analysis, we identify four distinct classes of polar textures in time-reversal-invariant systems, and we show that they carry integer topological charges. We validate this classfication by performing state-of-the-art first-principles calculations of materials representative of each class. For these materials, we compute the fingerprints of polaron topology in Huang diffuse scattering, and propose ultrafast electron and X-ray scattering experiments to detect these quasiparticles.

cond-mat.mtrl-sci↗

arXiv2026

Graphene-based technologies for energy applications, challenges and perspectives

Here we report on technology developments implemented into the Graphene Flagship European project for the integration of graphene and graphene-related materials (GRMs) into energy application devices. Many of the technologies investigated so far aim at producing composite materials associating graphene or GRMs with either metal or semiconducting nanocrystals or other carbon nanostructures (e.g., CNT, graphite). These composites can be used favourably as hydrogen storage materials or solar cell absorbers. They can also provide better performing electrodes for fuel cells, batteries, or supercapacitors. For photovoltaic (PV) electrodes, where thin layers and interface engineering are required, surface technologies are preferred. We are using conventional vacuum processes to integrate graphene as well as radically new approaches based on laser irradiation strategies. For each application, the potential of implemented technologies is then presented on the basis of selected experimental and modelling results. It is shown in particular how some of these technologies can maximize the benefit taken from GRM integration. The technical challenges still to be addressed are highlighted and perspectives derived from the running works emphasized.

cond-mat.mtrl-sci↗

arXiv2025

EPW-VASP interface for first-principles calculations of electron-phonon interactions

We present an interface between the Vienna \textit{Ab initio} Simulation Package (VASP) and the EPW software for calculating materials properties governed by electron-phonon (e-ph) interactions. Computation of the e-ph matrix elements with the finite-difference supercell approach in VASP and their fine-grid interpolation in EPW enable accurate modeling of temperature-dependent materials properties and phonon-assisted quantum processes with VASP's extensive library of exchange-correlation functionals and pseudopotentials. We demonstrate the functionality of the EPW-VASP interface by examining the superconducting gap and critical temperature in MgB$_2$ using the anisotropic Migdal-Eliashberg equations, and the carrier mobility in cubic BN using the \textit{ab initio} Boltzmann transport equation.

cond-mat.mtrl-sci↗

arXiv2025

Comparison between first-principles supercell calculations of polarons and the ab initio polaron equations

Polarons are composite quasiparticles formed by excess charges and the accompanying lattice distortions in solids, and play a critical role in transport, optical, and catalytic properties of semiconductors and insulators. The standard approach for calculating polarons from first principles relies on density functional theory and periodic supercells. An alternative approach consists of recasting the calculation of polaron wavefunction, lattice distortion, and energy as a coupled nonlinear eigenvalue problem, using the band structure, phonon dispersions, and the electron-phonon matrix elements as obtained from density functional perturbation theory. Here, we revisit the formal connection between these two approaches, with an emphasis on the handling of self-interaction correction, and we establish a compact formal link between them. We perform a quantitative comparison of these methods for the case of small polarons in the prototypical insulators TiO2, MgO, and LiF. We find that the polaron wavefunctions and lattice distortions obtained from these methods are nearly indistinguishable in all cases, and the formation energies are in good (TiO2) to fair (MgO) agreement. We show that the residual deviations can be ascribed to the neglect of higher-order electron-phonon couplings in the density functional perturbation theory approach.

cond-mat.mtrl-sci↗

arXiv2025

Comparative study of phonon-limited carrier transport in the Weyl semimetal TaAs family

We present a systematic first-principles study of phonon-limited transport in the TaAs family of Weyl semimetals using the ab initio Boltzmann transport equation. The calculated electrical conductivities show excellent agreement with experimental data for high-quality samples, confirming that transport in these systems is predominantly limited by phonon scattering. Among the four compounds, NbP achieves the highest conductivity, governed primarily by its large Fermi velocities that offset its stronger scattering rates. In contrast, TaAs displays the lowest conductivity, linked to reduced carrier pockets and limited carrier velocities. Additionally, NbP conductivity remains largely unaffected by small hole or electron doping, whereas TaAs exhibits pronounced electron-hole asymmetry. NbAs and TaP show intermediate behavior, reflecting their Fermi surface topologies and scattering phase space. These findings provide microscopic insight into the transport mechanisms of the TaAs family and emphasize the critical role of phonons, doping, and carrier dynamics in shaping their electronic response.

cond-mat.mes-hall↗

arXiv2025

Design of high-mobility p-type GaN via the piezomobility tensor

Gallium nitride (GaN) is a wide-bandgap semiconductor of significant interest for applications in solid-state lighting, power electronics, and radio-frequency amplifiers. An important limitation of this semiconductor is its low intrinsic hole mobility, which hinders the development of \textit{p}-channel devices and the large-scale integration of GaN CMOS in next-generation electronics. Prior research has explored the use of strain to improve the hole mobility of GaN, but a systematic analysis of all possible strain conditions and their impact on the mobility is lacking. In this study, we introduce a piezomobility tensor notation to characterize the relationship between applied strain and hole mobility in GaN. To map the strain-dependence of the hole mobility, we solve the \textit{ab initio} Boltzmann transport equation, accounting for electron-phonon scattering and GW quasiparticle energy corrections. We show that there exist three optimal strain configurations, two uniaxial strains and one shear strain, that can lead to significant mobility enhancement. In particular, we predict room-temperature hole mobility of up to 164~\mob\ for 2\% uniaxial compression and 148~\mob\ for 2\% shear strain. Our methodology provides a general framework for investigating strain effects on the transport properties of semiconductors from first principles.

cond-mat.mtrl-sci↗