A Quantum Monte Carlo Study of the Structural, Energetic, and Magnetic Properties of Two-Dimensional H and T phase VSe2
Daniel Wines, Juha Tiihonen, Kayahan Saritas, Jaron Krogel, Can Ataca
One of the most promising 2D ferromagnetic materials is monolayer VSe2 (T and H phase). Several works have controversially claimed near-room temperature ferromagnetism in VSe2, with conflicting results throughout the theoretical and experimental literature. These discrepancies in the electronic and magnetic properties between both phases of 2D VSe2 are most likely due to the structural parameters of each phase being coupled closely to the magnetic and electronic properties. Specifically, the T and H phases have a close lattice match and similar total energies, which makes it difficult to determine which phase is being observed experimentally. In this study, we used a combination of density functional theory (DFT), highly accurate diffusion Monte Carlo (DMC) and a recently developed surrogate Hessian line-search optimization technique to resolve the previously reported discrepancy in structural parameters and relative phase stability of 2D T-VSe2 and H-VSe2. With DMC accuracy, we determined the lattice constants and bond distances of both phases and found that H-VSe2 is more energetically favorable than T-VSe2 in freestanding form. We obtained a phase diagram between T and H phase from the potential energy surface (PES) and determined that a phase transition can be induced by strain or mechanisms such as thermal annealing. Finally, we benchmarked the magnetic properties such as spin density and magnetic moment per atom for both phases and find substantial differences between DMC and DFT. Our findings demonstrate the successes of the DMC method coupled with the surrogate Hessian structural optimization technique when applied to a 2D magnetic system. Our estimates for lattice constants, bond distances, relative phase energy and the extracted phase diagram assist in clarifying previously inconclusive results regarding T and H phase VSe2.
, Tiihonen, J.
, Saritas, K.
, Krogel, J.
and Ataca, C.
A Quantum Monte Carlo Study of the Structural, Energetic, and Magnetic Properties of Two-Dimensional H and T phase VSe2, Journal of Physical Chemistry Letters, [online], https://doi.org/10.1021/acs.jpclett.3c00497, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=935880
(Accessed December 8, 2023)