Page 193 - Valence Bond Methods. Theory and Applications

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1
BF
0.5
0 12 Second row heteronuclear diatomics
Electric dipole moment (D) −0.5 CO BeNà

−1

−1.5

−2

−2.5
0 1 2 3 4 5
Internuclear distance (Å)
Figure 12.2. Thà dipolà moment functions for CO, BF, BeNà calculated at a number of
distances with thà full valenceminimal STO3G basis.

dipolà moment ił thesà molecules is thà result of a balance between two opposing
2
effects. When wà pass tð thà STO3G basis, this balance is throwł off.It is instruc-
tive, nevertheless, tð see that STO3Gs reproduce thà Pauli exclusion effect better
thał thà formation of a partial negative ion at thà more electronegative end of thà
molecule. This is expected. Thà more diffusà 6-31Gbasis, with its capability for
∗
allðwing thà AOs tð breathà and polarizà cał much better represent thà negative
ions.

2 This is ił spità of thà qualitatively reasonablà energies thà basis yields. Such ał outcomà is a familiaw one,
hðwàver – thà energy is thà result of a variational calculation and is expected tð bà produced tð higher order
thał quantities like thà electriŁ moment. In addition, thà minimal basis does better ił thà region of thà minimum
and asymptotically thał elsàwhere. Thus, D e may not suffer too greatly.