关键词: Mn₂, spin polarization, density functional theory, potential function

Abstract: The density functional theory method (DFT) (b3p86) of Gaussian 03 has been used to optimize the structure of the Mn₂ molecule. The result shows that the ground state of the Mn₂ molecule is an 11-multiple state, indicating a spin polarization effect in the Mn₂ molecule, a transition metal element molecule. Meanwhile, we have not found any spin pollution because the wavefunction of the ground state does not mingle with wavefunctions of higher-energy states. So the ground state for Mn₂ molecule being of an 11-multiple state is the indicative of spin polarization effect of the Mn₂ molecule among those in the transition metal elements: that is, there are 10 parallel spin electrons in a Mn₂ molecule. The number of non-conjugated electrons is the greatest. These electrons occupy different spacious orbitals so that the energy of the Mn₂ molecule is minimized. It can be concluded that the effect of parallel spin in the Mn₂ molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell--Sorbie potential functions with the parameters for the ground state and other states of the Mn₂ molecule are derived. The dissociation energy D_e for the ground state of the Mn₂ molecule is 1.4477eV, equilibrium bond length R_e is 0.2506nm, vibration frequency $\omega$_e is 211.51cm^-1. Its force constants f₂, f₃, and f₄ are 0.7240aJ$\cdot$nm^-2, -3.35574aJ$\cdot$nm^-3, 11.4813aJ$\cdot$nm^-4 respectively. The other spectroscopic data for the ground state of the Mn₂ molecule $\omega$_e$\chi$_e, B_e, $\alpha$_e are 1.5301 cm^-1, 0.0978 cm^-1, 7.7825$\times$ 10^-4cm^-1 respectively.

Key words: Mn₂, spin polarization, density functional theory, potential function