The potential energy surface for spin-aligned Li3(1 4A′) and the potential energy curve for spin-aligned Li2(a 3Σu+)

Abstract

A global potential energy surface ͑PES͒ for the 1 4 AЈ spin-aligned state of Li 3 is presented. The surface is constructed as a many body expansion of the potential which is the sum of pairwise additive two-body potentials plus a three-body term. The two-body potential is that for the a 3 ⌺ u ϩ state of the lithium dimer. It combines the most recent Rydberg-Klein-Rees potential available ͓A. Ross ͑private communication͔͒ with well-known short and long range expansions and accurately reproduces all known experimental data. To obtain the three-body contributions, an ab initio PES was computed at 1122 points using full configuration interaction for the three valence electrons with an augmented Gaussian basis and the effective core potentials of Stevens, Basch, and Krauss ͓W. J. Stevens et al., J. Chem. Phys. 81, 6026 ͑1984͔͒ for the other electrons. The two-body interactions are also calculated using the same basis and then subtracted from the full interaction to give the three-body term. To construct the three-body potential at arbitrary configurations we use interpolation for small perimeters of the triangle formed by the triatomic system and an analytic fitting function for large perimeters. A switching function guarantees the smoothness of the potential function everywhere. The equilibrium position occurs at D 3h symmetry with a bond distance of 5.861a 0 , nearly 2a 0 smaller than the equilibrium value of 7.886a 0 of the lithium dimer. The well depth at the equilibrium is 4112.64 cm Ϫ1 . This is considerably deeper than the well depth of 1001.22 cm Ϫ1 for the pairwise additive potential at its equilibrium. Three-body effects are even more important for Li 3 than in the recently reported Na 3 case ͓J. Higgins et al., J. Chem. Phys. 112, 5751 ͑2000͔͒, and the nonadditive three-body term cannot be neglected in any calculation on this system.

Potential energy surface of the 12A′ Li2 + Li doublet ground state

“…To date, ab initio calculations for the sodium trimer have been done by several groups [8,9,10] as well as the potassium trimer [8,11,12]. In the case of lithium, the quartet ground state 1 4 A surface has been well studied [13,14,15,16] whereas the doublet system has been effectively ignored. The Jahn-Teller effect and conical intersections between the 1 2 E , 2 2 E and 1 2 A surfaces have been studied [17,18], as well as the vibrational [19], rovibrational [20] and hyperfine [21] structures of the lithium trimer.…”

UltracoldLi+Li2Collisions: Bosonic and Fermionic Cases

“…Our potential takes better account of this seam than that of ref. [16]. The methods we use to carry out quantum dynamics calculations on systems of this type have been described in our previous work on Na Na 2 [17,18] and elsewhere in the context of thermal reactive scattering [19], so a brief summary suffices here.…”

“…In the present work, we use a global Li 3 potential obtained from all-electron coupled-cluster electronic structure calculations, which will be described in detail elsewhere [15]. In parallel work, Colavecchia et al [16] have obtained another potential surface based on pseudopotential calculations. However, we chose to use our own surface in the present work because it takes better account of some features of the potential.…”

On the ro–vibrational energies for the lithium dimer; maximum-possible rotational levels

“…The discovery of Bose-Einstein condensation in some ultracold spin-polarized states of the alkali lithium dimer 7 Li 2 [1] has encouraged intensive experimental as well as theoretical studies on this system [2][3][4][5][6][7]. Whilst the Bose-Einstein condensation formation in 7 Li 2 dimer is found to depend on the interaction potential of the lowest triplet excited a 3 Σ + u state, its stability is observed to be sensitive to the binding energy of the least bound vibrational state (among the 11 vibrational states supported by the a 3 Σ + u -7 Li 2 potential) [2][3][4].…”