Cell Natural Orbitals in Quantum Materials

Harshitra Mahalingam; Nishchhal Verma; Daniel Muñoz-Segovia; Raquel Queiroz

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arXiv · 2608.10059

Cell Natural Orbitals in Quantum Materials

Harshitra Mahalingam·Nishchhal Verma·Daniel Muñoz-Segovia·Raquel Queiroz

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Abstract

Understanding correlated quantum matter starts with an accurate model of the single-particle states that interact at low energies: their dispersion, band geometry, orbital content and charge density. In many cases, notably the topological bands of moire materials, it is not straightforward to find a real-space description with a few local orbitals that accomplishes this task. Here we provide a systematic way to identify the local degrees of freedom that best capture the band geometry and charge density of any chosen set of bands. We use the unit-cell one-particle reduced density matrix (UC-1pRDM), obtained by restricting the projector onto the target bands to a single unit cell. Its eigenstates, which we call cell natural orbitals (CNOs), form a local, symmetric basis uniquely determined by the Bloch wavefunctions and the choice of real-space partition. Their eigenvalues measure the occupation of each CNO in the target bands, quantifying entanglement across unit-cell boundaries and the importance of multi-orbital character. A set of CNOs that maximizes total spectral weight and reproduces the target band symmetries provides optimal trial states for Wannierization. We exemplify this by constructing a lattice model for twisted bilayer WSe$_2$ that tracks the orbital content across twist angles.

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Harshitra Mahalingam, Nishchhal Verma, Daniel Muñoz-Segovia, Raquel Queiroz. 2026-08-10. Cell Natural Orbitals in Quantum Materials. https://arxiv.org/abs/2608.10059

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