A quasi-diabatic crystal orbital (CO) theory earlier developed has been applied to lithium heavily-doped trans-polyacetylene (t-PA) to study quasi-diabatic electronic effects in a metallic state. It has been shown that the quasi-diabatic electronic structure largely changes from the adiabatic electronic structure. This change arises from the strong interaction of the crystal momentum coupling between carbon pi and lithium canonical COs. The coupling also leads to occurrence of a large spin-density-wave (biradical character) in the quasi diabatic electronic state. The occurrence has been analyzed to be due to a large electron-electron repulsive interaction. The quasi-diabatic electronic structure has been discussed with a focus on the electron-electron repulsion.