Coherent state group-theoretic states

In order to make the END formalism practical, some approximations must be made in the representation of the waveffinctions of the electrons and nuclei. The particulars are outlined in the next section. In the simple model employed in this work, we choose to represent the electronic wavefunction by a group theoretical coherent states parametrization of a single determinant (SD). The nuclear wave function is formulated in terms of a frozen Gaussian wave packet (FGWP) and the limit of a narrow width is taken. This latter approximation corresponds to the classical limit for describing the nuclei. The coherent state representation of a single determinant leads to the so-called Thouless parametrization (29). For the description of the nuclear wavefunction, a quantum description has also been worked out (26, 30), but is yet to be implemented. 

On the electronic structure of the carbides of the group III elements (scandium, yttrium and the lanthanides), only a few theoretical investigations are available. The bond structure of ScC was calculated by Schwarz et al, (1969) using the augmented-plane-wave method, Ivashchenko et al, (1984) applied the same method to YC and presented the densities of states for YC,, = O-Sj 0-7 and 0.6, which were calculated by using the coherent potential approximation. The results have been used to analyze the stability of the compounds. However, both calculations (Schwarz et al. 1969, Ivashchenko et al. 1984) were not performed self-consistently. Zhukov et al. (1987)... 

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