关键词: Ni₂, spin polarization, density functional theory, potential function

Abstract: The density functional theory (DFT) method (b3p86) of Gaussian 03 is used to optimize the structure of the Ni₂ molecule. The result shows that the ground state for the Ni₂ molecule is a 5-multiple state, symbolising a spin polarization effect existing in the Ni₂ molecule, a transition metal molecule, but no spin pollution is found because the wave function of the ground state does not mingle with wave functions of higher-energy states. So the ground state for Ni₂ molecule, which is a 5-multiple state, is indicative of spin polarization effect of the Ni₂ molecule, that is, there exist 4 parallel spin electrons in Ni₂ molecule. The number of non-conjugated electrons is greatest. These electrons occupy different spatial orbitals so that the energy of the Ni₂ molecule is minimized. It can be concluded that the effect of parallel spin in the Ni₂ molecule is larger than that 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 of the ground state and other states of the Ni₂ molecule are derived. The dissociation energy D_e for the ground state of the Ni₂ molecule is 1.835eV, equilibrium bond length R_e is 0.2243 nm, vibration frequency $\omega$_e is 262.35 cm^-1. Its force constants f₂, f₃ and f₄ are 1.1901aJ.nm², --5.8723aJ.nm^-3, and 21.2505 aJ.nm^-4 respectively. The other spectroscopic data for the ground state of the Ni₂ molecule $\omega$_e$\chi$_e, B_e and $\alpha$_e are 1.6315cm^-1, 0.1141 cm^-1, and 8.0145x10^-4cm^-1 respectively.

Key words: Ni₂, spin polarization, density functional theory, potential function