Knowledge Bank

The Jahn-Teller effect on the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}E$ ground state of $VCl4$ has been investigated using ab initio restricted Hartree-Fock, CI calculations, and spin-orbit CI calculations with relativistic core potentials and gaussian double zeta plus polarization basis sets. The effects of the Jahn-Teller active E vibration were studied by computing the energy when opposite angles were simultaneously changed. The minimum energy occurs with opposite angles opened by $2.8\circ$, and is $97.4cm-1$ below the tetrahedral energy. Closing these angles by $2.6\circ$ corresponds to a saddle point on the surface which is $4.3cm-1$ higher in $energy.1$ Vibronic energies were calculated using generalized Born-Oppenheimer approximations and a harmonic oscillator expansion. The lowest energy level was found to be $6cm-1$ below the $Td$ energy. Thus this is an example of the dynamic Jahn-Teller case. The two-dimensional magnetic moment surface along the E vibrational coordinates was calculated and fitted to a second order equation. The magnetic moment of each vibronic state was then calculated using the vibronic wavefunction and the magnetic moment equation. The results showed a sizable effect of the vibronic interactions on the g factors. The two g factors are calculated to be 1.994 and 1.934 without the vibronic coupling, but change to 1.985 and 1.879 with the vibronic coupling effect considered. The calculated g factors agree with some but not all of the electron spin resonance data.