Basis Set Be Further Improved

Calculate the bond energy of H J by the G2 method in the GAUSSIAN implementation. 

The keyword is in the route section, line 1 of the input file. Lines 2, 3, and 4 are blank, comment, blank, respectively. Line 5 designates a charge of 1 and a spin multiplicity of 2 (a doublet). Line 6 specifies one atom as hydrogen, and line 7 specifies the second atom as hydrogen, attached to atom 1 at a distance of 1.32 A(2.49 bohr). Among several G2 energies printed out in about the last 25 lines of output are 

A distinction must be made between single-point GAUSSIAN calculations or optimizations and the energy output G2 (0 K). Individual GAUSSIAN calculations produce the energy coming out of the system when all the nuclei and electrons come together to form a molecule, radical, or ion, in this case. 

One may wonder why it is important to distinguish between and keep track of these two energies and Dq, when it seems that one would do. Actually, both are important. The bond energy Dg dominates theoretical comparisons and the dissociation energy Dq, which is the ground state of the real molecule, is used in practical applications like calculating thermodynamic properties and reaction kinetics. 

Even though the problem of the hydrogen molecule H2 is mathematically more difficult than, it was the first molecular orbital calculation to appear in the literature (Heitler and London, 1927). In contrast to Hj, we no longer have an exact result to refer to, nor shall we have an exact energy for any problem to be encountered from this point on. We do, however, have many reliable results from experimental thermochemistry and spectroscopy. 

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