The basis set convergence of the Hartree–Fock energy for H3 +, Li2 and N2

 By using completely optimized basis functions it is shown that the convergence of the Hartree–Fock energy for the H₃ ⁺, Li₂ and N₂ molecules is significantly better described by exponential behavior than by inverse power dependence. This is the case both with respect to the number of basis functions of a given type and with respect to the highest angular momentum function included. The Hartree–Fock limit for H₃ ⁺ is estimated to be −1.300372125 hartree. Received: 14 February 2000 / Accepted: 12 April 2000 / Published online: 18 August 2000     

Comment on: “Estimating the Hartree–Fock limit from finite basis set calculations” [Jensen F (2005) Theor Chem Acc 113:267]

We demonstrate that a minor modification of the extrapolation proposed by Jensen [(2005): Theor Chem Acc 113: 267] yields very reliable estimates of the Hartree–Fock limit in conjunction with correlation consistent basis sets. Specifically, a two-point extrapolation of the form yields HF limits E _HF,∞ with an RMS error of 0.1 millihartree using aug-cc-pVQZ and aug-cc-pV5Z basis sets, and of 0.01 millihartree using aug-cc-pV5Z and aug-cc-pV6Z basis sets.