Note
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SPARKLE¶
The lanthanides can be represented by their fully ionized 3+ sparkles.
That is, they have no basis set, and therefore cannot have a charge
different from +3.000. To use these sparkles, add keyword SPARKLE.
See also SPARKLES These entities do not need keyword
SPARKLE.
If SPARKLE is present, and it’s not needed, it will be ignored.
The geometries of the lanthanides are reproduced with good accuracy, but the heats of formation and electronic properties are not accurate.
To specify Dysprosium 3+ ion, use SPARKLE, and symbol Dy at the
appropriate point in the Z-matrix.
“f” Orbitals¶
Lanthanides 3+ ions have partially filled “f” shells, with the number of “f” electrons ranging from 0 (lanthanum) to 14 (lutetium). These electrons are important in the spectroscopy of Ln3+ complexes, where their excited states are represented in the UV-Vis spectra by quite sharp lines. That the lines are quite sharp indicates that the “f” electrons do not contribute significantly to covalent bonding. Therefore, in semiempirical methods, lanthanide ions are represented by an unpolarizable core consisting of the nucleus, all the electrons up to Xenon, and zero or more “4f” electrons. Only Ln3+ ions are available using the sparkle model, so the configurations used are La3+: [Xe]4f:sup:0; Ce3+: [Xe]4f:sup:1; … Lu3+: [Xe]4f:sup:14. Although not used in semiempirical theory, the ground states of these ions can be thought of as La3+: 1Sg; Ce3+: 2Fu; Pr3+: 3Hg; Nd3+: 4Ig; … Gd3+: 8Su;… Lu3+: 1Sg, but for computational convenience the ground states should be regarded as undefined, simply [Xe] plus zero, one, two or more “f” electrons. For this reason, when modeling Ln3+ complexes, ignore the atomic configuration of the Ln3+ ions, instead pay attention only to the electronic state of the rest of the system. For most simple organics, such as lanthanum trisacetylacetonate, CSD entry AQACAL, this will be the Singlet; almost all others will be Doublets. For these sets, explicit keywords are not needed - they will be automatically recognized by default. Only for exotic systems, such as Triplet or excited states would keywords defining the state be needed.