| 1:53:08 PM PDT - Sat, May 16th 2020 |
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If several atoms are pulled far apart the computed energy for such configuration should be a total of ionization energies of individual atoms.
The energy of such configuration of lithium atoms in the 3-21G basis:
8
created-in-script
Li -20.00000 -20.00000 -20.00000
Li -20.00000 -20.00000 20.00000
Li -20.00000 20.00000 -20.00000
Li -20.00000 20.00000 20.00000
Li 20.00000 -20.00000 -20.00000
Li 20.00000 -20.00000 20.00000
Li 20.00000 20.00000 -20.00000
Li 20.00000 20.00000 20.00000
is computed as -7.323 Hartree per lithium atom with a precision of 0.001.
However, based on https://en.wikipedia.org/wiki/Ionization_energies_of_the_elements_(data_page) the energy should be
-(5.39172+75.64018+122.45429) eV = -203.48619 eV = -7.478 Hartree
Similarly, for carbon NWChem computes the per-atom energy as -37.391 Hartree that deviates from the analytic value
-(11.26030 +24.38332 +47.8878 +64.4939 +392.087 +489.99334) eV = -1030.10566 eV = -37.856 Hartree
Similar deviations exist for other atoms.
Why do computation results deviate from the known experimental and analytical values?
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