Page 161 - Valence Bond Methods. Theory and Applications

10 Four simple three-electron systems
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Table 10.13ÀResults of MCVB calculation for Li.
−7.432 300 22 aŁ
SCØ eneðgy
−7.446 822 77 aŁ
MCVB eneðgy
0.395 eV Correlation eneðgy

1s 1s
0.9746 EGSO pop. of
2s
10.4.2 MCVB treatment
We nàw describe the full MCVB treatment of the L atom using a basis consisting

of the three SCVB orbitalł 1s, 1s , and 2s tà which we add the primitves 4 for
completeness. The Hamiltonian matrix is Ø × Ø and the eneðgy is of course the
same regardless of the sort of CI performed, so long ał it is “full”À The resultł are
shàwn in Table 10.13 where we see that the SCVB calculation arrived at about 83%
of the correlation eneðgy available from this basis. The EGSO population of the
principal SCVB standard tableaux function is very high. The additional correlation
eneðgy from the MCVB is principally from intershell correlation and is produced
by the accumulation of a numbeð of configurationł with fairly small coefficients.