arXiv subjects

Tommaso Gorni

Publications and source records attributed to Tommaso Gorni.

13 recordsLinked to original sources

arXiv2025

Tunable Electronic Correlations in 135-Kagome Metals

Kagome metals exhibit rich correlated-electron physics, yet a systematic understanding of the degree of correlation across transition-metal species remains elusive. Using density-functional theory plus multi-orbital slave-spin mean-field theory, we investigate electronic correlations in the Ti-, V-, and Cr-based 135 compounds with Sb and Bi pnictogens. We find that the significantly stronger degree of correlation of the Cr-based materials compared to Ti and V can only be explained through the synergy of two effects: the larger electron filling of the $d$-shell and the reduced characteristic kinetic energy. We put forward that the substitution of Sb with Bi strengthens correlations in all compounds and make the prediction that the-yet-to-be-synthesized CsCr$_3$Bi$_5$ must be the most strongly correlated member of the entire family. These findings provide a quantitative, band-structure-based framework for understanding and predicting correlation strength in Kagome metals.

cond-mat.str-el↗

arXiv2025

QMCkl: A Kernel Library for Quantum Monte Carlo Applications

Quantum Monte Carlo (QMC) methods deliver highly accurate electronic structure calculations but are computationally intensive. The quantum Monte Carlo kernel library (QMCkl) provides a modular, portable collection of high-performance kernels implementing the core building blocks of QMC calculations. It offers a C-compatible API, supports the TREXIO standard for input, and covers essential QMC kernels including atomic and molecular orbitals, cusp corrections, Jastrow factor, and the necessary derivatives also to perform variational and structural optimization. QMCkl separates algorithmic development from hardware-specific tuning by combining human-readable reference implementations with performance-optimized kernels that produce identical numerical results. The library enables consistent, efficient, and reproducible simulations across different QMC codes and architectures, and achieves substantial speedups in the evaluation of the energy and its derivatives. Beyond QMC, QMCkl can accelerate deterministic quantum chemistry workflows and visualization tools, promoting cross-code interoperability and simplifying high-performance scientific software development.

physics.chem-ph↗

arXiv2025

Local-moment magnetism in Mn-based pnictides

We report a comprehensive study of electronic-correlation effects in Manganese-based antiferromagnetic pnictides BaMn$_2$Pn$_2$ (Pn=P,As,Sb,Bi). Our density functional theory plus slave-spin mean-field simulations indicate that all the compounds lie on the strong-coupling side of an itinerant-to-localized moment crossover, corresponding to the critical interaction strength for the Mott transition in the high-temperature paramagnetic phase. We also show that the experimental Néel temperature of each compound scales with the distance from this crossover.

cond-mat.str-el↗

arXiv2023

Magnon-phonon interactions enhance the gap at the Dirac point in the spin-wave spectra of CrI$_3$ two-dimensional magnets

Recent neutron-diffraction experiments in honeycomb CrI$_3$ quasi-2D ferromagnets have evinced the existence of a gap at the Dirac point in their spin-wave spectra. The existence of this gap has been attributed to strong in-plane Dzyaloshinskii-Moriya or Kitaev (DM/K) interactions and suggested to set the stage for topologically protected edge states to sustain non-dissipative spin transport. We perform state-of-the-art simulations of the spin-wave spectra in monolayer CrI$_3$, based on time-dependent density-functional perturbation theory (TDDFpT) and fully accounting for spin-orbit couplings (SOC) from which DM/K interactions ultimately stem. While our results are in qualitative agreement with experiments, the computed TDDFpT magnon gap at the Dirac point is found to be 0.47~meV, roughly 6 times smaller than the most recent experimental estimates, so questioning that intralayer anisotropies alone can explain the observed gap. Lattice-dynamical calculations, performed within density-functional perturbation theory (DFpT), indicate that a substantial degeneracy and a strong coupling between vibrational and magnetic excitations exist in this system, providing a possible additional gap-opening mechanism in the spin-wave spectra. In order to pursue this path, we introduce an interacting magnon-phonon Hamiltonian featuring a linear coupling between lattice and spin fluctuations, enabled by the magnetic anisotropy induced by SOC. Upon determination of the relevant interaction constants by DFpT and supercell calculations, this model allows us to propose magnon-phonon interactions as an important microscopic mechanism responsible for the enhancement of the gap in the range of $\approx 4$~meV around the Dirac point of the CrI$_3$ monolayer.

cond-mat.mtrl-sci↗

arXiv2023

Paradigm for finding d-electron heavy fermions: the case of Cr-doped CsFe$_2$As$_2$

We define a general strategy for finding new heavy-fermionic materials without rare-earth elements: doping a Hund metal with pronounced orbital-selective correlations towards half-filling. We argue that in general band structures a possible orbital-selective Mott transition is frustrated by inter-orbital hopping into heavy-fermion behaviour - where d-orbitals provide both the heavy and the light electrons - which is enhanced when approaching half-filling. This phase ultimately disappears due to magnetic correlations, as in a standard Doniach diagram. Experimentally we have further hole doped CsFe$_2$As$_2$, a Hund metal with 0.5 electrons/Fe away from half-filling, and obtained a heavy fermionic state with the highest Sommerfeld coefficient for Fe-pnictides to date (270 mJ/mol K$^2$), before signatures of an antiferromagnetic phase set in.

cond-mat.str-el↗

arXiv2023

First-principles study of the gap in the spin excitation spectrum of the CrI$_3$ honeycomb ferromagnet

The nature of the gap observed at the zone border in the spin-excitation spectrum of CrI$_3$ quasi-2D single crystals is still controversial. We perform first-principles calculations based on time-dependent density-functional perturbation theory, which indicate that the observed gap results from a combination of spin-orbit and inter-layer interaction effects. The former give rise to the anisotropic spin-spin interactions that are responsible for its very existence, while the latter determine both its displacement from the K point of the Brillouin zone due to the in-plane lattice distortions induced by them, and an enhancement of its magnitude, in agreement with experiments and previous theoretical work based on a lattice model.

cond-mat.mtrl-sci↗

arXiv2023

Slave-spin mean field for broken-symmetry states: Néel antiferromagnetism and its phase separation in multi-orbital Hubbard models

We introduce the generalization of the Slave-Spin Mean-Field method to broken-symmetry phases. Through a variational approach we derive the single-particle energy shift in the mean-field equations which generates the appropriate self-consistent field responsible for the stabilization of the broken symmetry. With this correction the different flavours of the slave-spin mean-field are actually the same method and they give identical results to Kotliar-Ruckenstein slave-bosons and to the Gutzwiller approximation. We apply our formalism to the Néel antiferromagnetic state and study it in multi-orbital models as a function of the number of orbitals and Hund's coupling strength, providing phase diagrams in the interaction-doping plane. We show that the doped antiferromagnet in proximity of half-filling is typically unstable towards insulator-metal and magnetic-non magnetic phase separation. Hund's coupling extends the range of this antiferromagnet, and favors its phase separation.

cond-mat.str-el↗

arXiv2023

Manipulation of the magnetic state of a porphyrin-based molecule on gold: From Kondo to quantum nanomagnet via the charge fluctuation regime

By moving individual Fe-Porphyrin-based molecules with the tip of Scanning Tunneling Microscope in the vicinity of a Br-atom containing elbow of the herringbone-reconstructed Au(111), we reversibly and continuously control their magnetic state. Several regimes are obtained experimentally and explored theoretically: from the integer spin limit, through intermediate magnetic states with renormalized magnetic anisotropy, until the Kondo-screened regime, corresponding to a progressive increase of charge fluctuations and mixed valency due to an increase in the interaction of the molecular Fe states with the substrate Fermi sea. Our results open a route for the realization, tuning and experimental studies of novel quantum magnetic states in molecule-surface hybrids.

cond-mat.mes-hall↗

arXiv2022

Rationalizing doping and electronic correlations in LaFe$_2$As$_2$

We compute the electronic properties of the normal state of uncollapsed LaFe$_2$As$_2$, taking into account local dynamical correlations by means of slave-spin mean-field+density-functional theory. Assuming the same local interaction strength used to model the whole electron- and hole-doped BaFe$_2$As$_2$ family, our calculations reproduce the experimental Sommerfeld specific heat coefficient, which is twice the value predicted by uncorrelated band theory. We find that LaFe$_2$As$_2$ has a reduced bare bandwidth and this solves the apparent paradox of its sizeable correlations despite its nominal valence d$^{6.5}$, which would imply extreme overdoping and uncorrelated behaviour in BaFe$_2$As$_2$. Our results yield a consistent picture of the whole 122 family and point at the importance of the correlation strength, rather than sheer doping, in the interpretation of the phase diagram of iron-based superconductors

cond-mat.supr-con↗

arXiv2022

turboMagnon -- A code for the simulation of spin-wave spectra using the Liouville-Lanczos approach to time-dependent density-functional perturbation theory

We introduce turboMagnon, an implementation of the Liouville-Lanczos approach to linearized time-dependent density-functional theory, designed to simulate spin-wave spectra in solid-state materials. The code is based on the noncollinear spin-polarized framework and the self-consistent inclusion of spin-orbit coupling that allow to model complex magnetic excitations. The spin susceptibility matrix is computed using the Lanczos recursion algorithm that is implemented in two flavors - the non-Hermitian and the pseudo-Hermitian one. turboMagnon is open-source software distributed under the terms of the GPL as a component of Quantum ESPRESSO. As with other components, turboMagnon is optimized to run on massively parallel architectures using native mathematical libraries (LAPACK and FFTW) and a hierarchy of custom parallelization layers built on top of MPI. The effectiveness of the code is showcased by computing magnon dispersions for the CrI$_3$ monolayer, and the importance of the spin-orbit coupling is discussed.

physics.comp-ph↗

arXiv2021

Accurate modeling of FeSe with screened Fock exchange and Hund's metal correlations

We reproduce the electronic properties of FeSe in the high-temperature phase within an ab initio framework that includes screened Fock exchange and local dynamical correlations. We robustly capture the experimental band structure, as long as the system is in the Hund's metal phase. In particular, we account for the shrinking of the Fermi pockets and the sinking below the Fermi level of the hole pocket with $xy$ orbital character. This entails the elusive correct estimate of the Sommerfeld coefficient, and supports the interpretation of non-compensated Fermi pockets seen in ARPES in terms of surface electron doping. More stringently, our modeling matches well the experimental interband optical spectrum, and captures qualitatively the temperature dependence of the thermoelectric power, extremely sensitive to the details of the bands around the Fermi level.

cond-mat.str-el↗

arXiv2019

Epsilon-iron as a spin-smectic state

Using x-ray emission spectroscopy, we find appreciable local magnetic moments until 30-40 GPa in the high-pressure phase of iron, however no magnetic order is detected with neutron powder diffraction down to 1.8 K contrary to previous predictions. Our first-principles calculations reveal a "spin-smectic" state lower in energy than previous results. This state forms antiferromagnetic bilayers separated by null spin bilayers, which allows a complete relaxation of the inherent frustration of antiferromagnetism on a hexagonal close-packed lattice. The magnetic bilayers are likely orientationally disordered, owing to the soft interlayer excitations and the near-degeneracy with other smectic phases. This possible lack of long-range correlation agrees with the null results from neutron powder diffraction. An orientationally-disordered, spin-smectic state resolves previously perceived contradictions in high pressure iron and could be integral to explaining its puzzling superconductivity.

cond-mat.mtrl-sci↗

arXiv2018

Spin dynamics from time-dependent density functional perturbation theory

We present a new method to model spin-wave excitations in magnetic solids, based on the Liouville-Lanczos approach to time-dependent density functional perturbation theory. This method avoids computationally expensive sums over empty states and naturally deals with the coupling between spin and charge fluctuations, without ever explicitly computing charge-density susceptibilities. Spin-wave excitations are obtained with one Lanczos chain per magnon wave-number and polarization, avoiding the solution of the linear-response problem for every individual value of frequency, as other state-of-the-art approaches do. Our method is validated by computing magnon dispersions in bulk Fe and Ni, resulting in agreement with previous theoretical studies in both cases, and with experiment in the case of Fe. The disagreement in the case of Ni is also comparable with that of previous computations.

cond-mat.mtrl-sci↗