Predicted ground states

We presented selected results from a new tight-binding total energy method that accurately predicts ground state properties of transition and noble metals, and successfully extended to transition metal carbides. 

The corresponding lanthanide allyl, Sm(C5H5)2(allyl), has recently been reported and preliminary indications, based upon the absence of infrared absorptions in 1610—1640 cm i region, are consistent with a jr-bonded structure 149). Since the jr-bonded structure would be formally eight coordinate and the a-bonded structure only six coordinate, this would be the predicted ground state. 

This theory also possesses an ab initio based quantitative version (10,19), in which the parameters are geometry dependent and fitted on accurately calculated potential surfaces of ethylene. Despite its simplicity, the spin-Hamiltonian theory has proven itself to be accurate for predicting ground state, as well as excited state, properties and transition energies. 

Bonding in dimer 125 of a diphosphirenyl radical was analyzed by ab initio calculations for the parent system XIII. For the monomeric radical the calculations predicted ground state as illustrated by the canonical structures XIV and XrV (Figure 3). 

A number of further ab initio calculations [33 to 40] and one semiempirical (CNDO) study [41] dealt with geometry optimization for PH and predicted ground-state and, in one case [38], excited-state equilibrium internuclear distances. 

In accordance with these predictions, ground-state triatomics with 16 or fewer valence electrons (CO2, CS2, OCS, N2O) are experimentally found to be linear, while those with more than 16 valence electrons (NO2, O3, SO2) are bent. 

Tautermann CS, Voegele AF, Loerting T, Liedl KL (2002) An accurate semiclassical method to predict ground-state tunnehng splittings. J Chem Phys 117 1967... 

A semiempirical method can be designed to predict some phenomena more accurately than others. Thus, MNDO (see MNDO) was designed to predict ground-state properties. It does this well, but when the method is applied to excited states, the accuracy of prediction of UV-VIS spectra is very poor. Other methods, particularly ZINDO (a parameterized INDO technique), predict such spectra with quite high accuracy, but in turn these methods are poor at predicting ground-state phenomena, such as geometries or heats of formation. 

Since the open-shell term in P does not possess spherical symmetry, the effective Hamiltonian will contain a non-spherical potential and as a result, even with initial orbitals of true central-field form (i.e. with spherical-harmonic angle dependence), the first cycle of an SCF iteration will destroy the symmetry properties of the orbitals—the solutions that give an improved energy will not be of pure s and p type but will be mixtures. This is a second example of a symmetry-breaking situation, akin to the spin polarization encountered in the UHF method. The resultant many-electron wavefunction will also lose the symmetry characteristic of a true spectroscopic state there will be a spatial polarization of the Is 2s core and the predicted ground state will no longer be of pure P type, just as in the UHF calculation there will be a spin polarization and the exact spin multiplicity of the many-electron state will be lost. Of course, the many-electron Hamiltonian does possess spherical symmetry (i.e. invariance under rotations around the nucleus), and the reason for the symmetry breaking lies at the level of the one-electron (i.e. IPM-type) model—the effective field in the 1-electron Hamiltonian is a fiction rather than a reality. 

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