Three-body harmonic molecule

• Published in: Journal of physics. B, Atomic, molecular, and optical physics Atomic, molecular, and optical physics, 2023-04, Vol.56 (7), p.75002
• Main Authors: Olivares-Pilón, H, Escobar-Ruiz, A M, Molina, F Montoya
• Format: Article
• Language: English
• Subjects: harmonic molecule; integrability; Lagrange-mesh method; perturbation theory
• ISSN: 0953-4075; 1361-6455
• DOI: 10.1088/1361-6455/acbdf0

In this study, the quantum three-body harmonic system with finite rest length R and zero total angular momentum L  = 0 is explored. It governs the near-equilibrium S -states eigenfunctions ψ ( r 12 , r 13 , r 23 ) of three identical point particles interacting by means of any pairwise confining potential V ( r 12 , r 13 , r 23 ) that entirely depends on the relative distances r i j = | r i − r j | between particles. At R  = 0, the system admits a complete separation of variables in Jacobi-coordinates, it is (maximally) superintegrable and exactly-solvable. The whole spectra of excited states is degenerate, and to analyze it a detailed comparison between two relevant Lie-algebraic representations of the corresponding reduced Hamiltonian is carried out. At R  > 0, the problem is not even integrable nor exactly-solvable and the degeneration is partially removed. In this case, no exact solutions of the Schrödinger equation have been found so far whilst its classical counterpart turns out to be a chaotic system. For R  > 0, accurate values for the total energy E of the lowest quantum states are obtained using the Lagrange-mesh method. Concrete explicit results with not less than eleven significant digits for the states N = 0 , 1 , 2 , 3 are presented in the range 0 ⩽ R ⩽ 4.0  a.u. In particular, it is shown that (I) the energy curve E = E ( R ) develops a global minimum as a function of the rest length R , and it tends asymptotically to a finite value at large R , and (II) the degenerate states split into sub-levels. For the ground state, perturbative (small- R ) and two-parametric variational results (arbitrary R ) are displayed as well. An extension of the model with applications in molecular physics is briefly discussed.