arXiv subjects

Maristella Alessio

Publications and source records attributed to Maristella Alessio.

4 recordsLinked to original sources

arXiv2026

Coupled-cluster study of dynamic Jahn-Teller effect in a $5d^2$ W antifluorite

In correlated insulators, the interplay among coexisting charge, spin, orbital, and lattice degrees of freedom gives rise to rich quantum phenomena, while unraveling the interplay is not straightforward. In the family of cubic $5d^2$ double perovskites, the ground spin-orbit coupled electronic states of $5d$ metal sites are degenerate and couple to the Jahn-Teller active vibrations, whereas no experimental evidence of the symmetry-lowering in the low-temperature ordered phases has been reported. To quantitatively unravel the nature of $5d^2$ centers, we apply equation-of-motion coupled cluster (EOM-CC) theory to analyze the vibronic and magnetic properties of $5d^2$ W sites of Cs$_2$WCl$_6$. We derive the electronic and vibronic model Hamiltonians, calculate the W $L_3$ edge resonant inelastic x-ray scattering (RIXS) spectra, and determine the effective magnetic moment. The simulated RIXS spectra show that vibronic coupling makes several peaks asymmetric. The effective magnetic moments exhibit a temperature dependence similar to that observed experimentally, confirming the validity of the calculated distribution of low-energy levels. Our calculations indicate that the Jahn-Teller effect in Cs$_2$WCl$_6$ is in a weak regime, and noticeable deformation would not occur, whereas the dynamic Jahn-Teller effect modulates the shapes of the RIXS spectra and affects the magnetic moment. This work demonstrates the usefulness of the EOM-CC method for predicting physical phenomena on metal sites in correlated insulating materials.

cond-mat.str-el↗

arXiv2026

Coupled-cluster approach to vibronic effects in resonant inelastic x-ray scattering of quantum materials: Application to a $5d^1$ rhenium oxide

First-principles analysis of the spectroscopic signatures of correlated quantum materials poses significant challenges due to the interplay between spin-orbit and vibronic couplings, as well as the need to describe both dynamic and static electron correlation to reach decent accuracy. In this work, we apply the equation-of-motion coupled-cluster (EOM-CC) method to derive the spin-orbit-lattice entangled vibronic states and predict the Re $L_3$ edge resonant inelastic x-ray scattering (RIXS) spectra of Ba$_2$MgReO$_6$. The EOM-CC yields interaction parameters in close agreement with those extracted from RIXS spectra, with errors of less than 5\%. In particular, the EOM-CC method allowed us to determine the weak vibronic coupling to the $T_{2g}$ vibrations, which is difficult to address experimentally. The simulated spectra indicate that vibronic coupling to the $T_{2g}$ modes gives rise to a shoulder on the elastic peak. Going beyond the conventional treatment, which focuses solely on $E_g$ modes, we show that vibronic couplings to both $T_{2g}$ and $E_g$ modes are required to account for the fine structure of the RIXS spectra. This work demonstrates that the EOM-CC method is a powerful tool for accurately predicting the complex local states at metal sites and spectroscopic signatures of correlated insulating materials.

cond-mat.str-el↗

arXiv2024

Dissociative Electron Attachment on Metal Surfaces: The Case of HCl$^-$ on Au(111)

The transfer of charges, including electrons and holes, is a key step in heterogeneous catalysis, taking part in the reduction and oxidation of adsorbate species on catalyst surfaces. In plasmonic catalysis, electrons can transfer from photo-excited metal nanoparticles to molecular adsorbates, forming transient negative ions that can easily undergo reactions such as dissociation, desorption, or other chemical transformations. However, ab initio characterization of these anionic states has proven challenging, and little is known about the topology of their potential energy surfaces. In this work, we investigate the dissociative adsorption of HCl on Au(111) as a representative catalytic process with relatively low reaction probabilities, which could potentially be enhanced by electron transfer from photo-excited gold nanoparticles to HCl. We employ projection-based density embedding that combines the equation-of-motion electron-attachment coupled-cluster singles and doubles (EOM-EA-CCSD) method with density functional theory (DFT), and build dissociation curves of HCl$^-$ on Au(111) along the H-Cl bond distance. The HCl anion in the gas phase is unbound at equilibrium distances and only becomes bound as the bond stretches. However, our results show that, upon adsorption on Au(111), HCl$^-$ remains a stable, bound anion at all bond lengths due to charge delocalization to the metal. Forming bound anions is easier, and dissociation of HCl$^-$ on Au(111) is further facilitated, with its dissociation energy reduced by 0.61 eV compared to its neutral counterpart on Au(111), and by 1.16 eV relative to HCl. These results underscore the efficacy of embedded EOM-CCSD methods in addressing surface science challenges and highlight the potential of plasmonic catalysis proceeding via bound, rather than transient, anionic states.

cond-mat.mtrl-sci↗

arXiv2024

Signatures of s-wave scattering in bound electronic states

We compute EOM-EA-CCSD and EOM-EA-CCSDT potential energy curves and one-electron properties of several anions at bond lengths close to where these states become unbound. In the potential energy curves of the totally symmetric anions of HCl and pyrrole, which are associated with s-wave scattering states at the equilibrium bond lengths of the parent neutral molecules, we observe on inclusion of diffuse basis functions a pronounced bending effect near the crossing points with the potential energy curves of the neutral molecules. Additionally, we observe that the Dyson orbital and second moment of the electron density become extremely large in this region. In particular, the second moment of the HCl anion becomes 5 orders of magnitude times larger over a range of 5 pm. This behaviour is very different to the well-characterised non-totally symmetric anions of dinitrogen and dihydrogen that correspond to electronic resonances at the equilibrium bond lengths of their parent neutral molecules. Our work thus shows that bound state electronic-structure methods can distinguish between anions that turn into electronic resonances and those associated with s-wave scattering states.

physics.chem-ph↗