arXiv subjects

Kushantha P. K. Withanage

Publications and source records attributed to Kushantha P. K. Withanage.

3 recordsLinked to original sources

arXiv2026

A systematic study of single molecule metallocenes with 4d and 3d transition metal atoms

The realization of spin-based devices remains one of the central goals of spintronics research. Single-molecule magnets (SMMs) constitute an important class of nanoscale magnetic systems with significant potential for spintronic applications, where individual molecules can serve as fundamental building blocks of functional devices. In this work, we systematically investigate a family of 4d and 3d transition-metal metallocenes using first-principles density functional theory. Among the seven 4d metallocenes considered, only Mo and Rh metallocenes undergo Jahn Teller distortions and exhibit uniaxial anisotropy with energy barriers of approximately 20 K. Similarly, among the 3d metallocenes studied in this work, only Cr and Co metallocenes undergo Jahn Teller distortions and display uniaxial anisotropy, although with smaller barriers below 10 K. All remaining metallocenes exhibit easy-plane anisotropy. We find that the magnetic anisotropy energy does not increase monotonically with the number of d electrons; instead, it is governed primarily by the orbital ordering of the transition-metal d states. Our calculations further show that the Jahn Teller distortion induces transverse anisotropy, leading to zero-field magnetization tunneling across the energy barrier, with the weakest tunneling rate for Mo metallocene. For the Mo metallocene, the magnetic anisotropy energy increases to approximately 60 K in cationic charge states, although the magnetic anisotropy changes from uniaxial to easy-plane. In this work, we also investigate the influence of ligand size on the structural stability of metallocenes and establish practical guidelines for constructing reliable molecular models for first-principles studies. Finally, we also propose that metallocenes with easy-plane anisotropy could serve as magnetic sensing elements, highlighting their potential beyond memory applications.

cond-mat.mtrl-sci↗

arXiv2025

Universal Approach for Determining Multi-Dimensional Anharmonic Vibrations from Electronic Quantum Methods

We present a simple and efficient method to incorporate anharmonic effects in the vibrational \textcolor{black}{analyses} of molecules within density functional theory (DFT) calculations. This approach is closely related to the traditional vibrational \textcolor{black}{configuration} interaction (VCI) technique, which uses the harmonic oscillator wavefunctions as the basis. In our implementation, we employ Gaussian-type orbitals (GTOs), with polynomial prefactors, as the basis set to evaluate the anharmonic Hamiltonian. Although these basis functions are non-orthogonal, the matrix elements such as overlap, kinetic energy terms, and position moments can be evaluated analytically. The terms in the Hamiltonian due to the anharmonic potentials are numerically calculated on a Hermite-Quadrature grid. The potentials can be evaluated using any electronic structure method. This framework enables us to accurately calculate the anharmonicity-corrected vibrational frequencies, the fundamental frequencies, and the corrections to bond lengths in diatomic molecules. This method is also generalized to handle coupled anharmonic oscillators, which is essential to model more complex phenomena such as nitrogen tunneling in the umbrella mode of ammonia (NH$_3$) and Fermi resonances in carbon dioxide (CO$_2$).

physics.chem-ph↗

arXiv2024

Non-collinear first-principles studies of the spin-electric coupling in frustrated triangular molecular magnets

Frustrated triangular molecular magnets (MMs) with anti-ferromagnetic ground states (GS) are an important class of magnetic systems with potential applications in quantum information processing. The two-fold degenerate GS of these molecules, characterized by spin chirality, can be utilized to encode qubits for quantum computing. Furthermore, because of the lack of inversion symmetry in these molecules, an electric field couples directly states of opposite chirality, allowing a very efficient and fast control of the qubits. In this work we present a theoretical method to calculate the spin-electric coupling for triangular MMs with effective {\it local} spins $s$ larger than 1/2, which is amenable to a first-principles implementation based on density functional theory (DFT). In contrast to MMs where the net magnetization at the magnetic atoms is $μ_{\rm B}/2$ ($μ_{\rm B} $ is the Bohr magneton), the DFT treatment of frustrated triangular MMs with larger local magnetizations requires a fully non-collinear approach, which we have implemented in the NRLMOL DFT code. As an example, we have used these methods to evaluate the spin-electric coupling for a spin $s = 5/2$ $\{\mathrm{Fe_3}\}$ triangular MM, where this effect has been observed experimentally for the first time quite recently. Our theoretical and computational methods will help elucidate and further guide ongoing experimental work in the field of quantum molecular spintronics.

cond-mat.mes-hall↗