Electronic properties of alkali trimers

Abstract

The electronic properties of the alkali trimers Li3, Na3, and K3 are studied using the pseudopotential and the local-spin-density approximations. More than 100 configurations were calculated for each trimer in order to obtain a complete picture of the adiabatic Born–Oppenheimer surfaces. The equilibrium geometry of the trimers are Jahn–Teller distortions of an equilateral triangle. Although the three surfaces are quite similar, Li3 is more affected than Na3 or K3 by the dynamical character of the Jahn–Teller distortion. The calculated ionization potentials agree very well with the experimental values and the qualitative features of the Born–Oppenheimer surface are confirmed by recent ESR experiments.

General properties of the electronic structure of alkali metal clusters and Ia-IIa mixed clusters

“…The absolute values of the calculated binding energy per atom are substantially smaller for Na n than for Lin clusters. For comparison, Eb/n functions for sodium clusters obtained with the local spin density method (LSD) by Martins et al [14][15][16] are also drawn in Fig. 3.…”

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.…”

A diabatic representation of the two lowest electronic states of Li3

“…The energy of the conical intersection, V 0a , reveals a harmonic dependence of the Q s coordinate reflecting the symmet-ric normal mode vibration. We obtain a vibrational frequency of ω a = 368.2 cm −1 , which should be compared with previous theoretical predictions of 349 cm −1 [14] and 327 cm −1 [16]. …”

“…The simplest example of such a situation is given by the E ⊗ ε Jahn-Teller (JT) effect [1] with a conical intersection involving the two-fold degenerate electronic states E with the doubly degenerate nuclear vibration modes ε. Alkali metal trimers X 3 with a conical intersections at the geometric D 3h symmetries are special cases of the E ⊗ ε JT systems [2]. As a result, in recent years small metal clusters have received great attention as the subject of many experimental [3][4][5][6][7][8][9][10][11][12] and theoretical [2,[13][14][15][16][17][18][19][20] publications. These systems are especially convenient for experimental studies due to their possibility of vibrational excitation in the visible or near infrared regions [21].…”

“…Already in 1978, Gerber et al [14] computed the lowest adiabatic potential energy surface as a function of the normal mode coordinates using the coupled * Electronic address: aasal@fysik.su.se electron pair approximation (CEPA). The lowest adiabatic potential energy surface has also been calculated by applying density functional theory with a pseudopotential approximation [16]. Using the Multi-Reference Configuration Interaction (MRCI) method, Ehara et al [22] calculated the full three-dimensional potential energy surfaces of the first and second adiabatic states.…”