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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- 

