2 4 8 16 32 R  (a.u.) -1,7 -1,69 -1,68 -1,67 -1,66 -1,65 -1,64 -1,63 Energy (a.u.) -1,702 -1,7 8 16 32 -1,70168 -1,70167 r =1.4 r=1.6 r =1.2 r =1.8 ) r =2.0 r =1.0 r =2.2 R r (b) (a) (c) FIG. 5: (Color online) Same as Fig. 3 except γ = 90 ° . The two insets, (b) and (c), show the behavior of the potentials for r = 1 . 4 a.u. on two different magnification scales: Region (b) is the magnified version of (a), region (c) is magnified (b). contribution is positive and C$_{4}$/R 4 is negative (see Eq. 1). Therefore, their sum combined with the short-range interaction produces a potential curve (for fixed r and γ near 90 ° ) that has a pronounced minimum in PES-PS and just a should-like feature in the present PES (see inset (c) in Fig. 5). The curve is repulsive asymptotically. A possible reason for the above differences is the somewhat smaller basis set (d-aug-cc-PVTZ) used in calculation of PES-PS [11]. The numerical data available about PES-BT [19, 23] is given in Table I. Since the calcula- 11