The block-localized wavefunction (BLW) method, which can turn off the electron delocalization in molecules, is introduced. To construct the wave function for a strictly localized structure (or a diabatic state), all electrons and primitive orbitals are partitioned into several subspaces, and each molecular orbital is expanded in only one subspace. While the molecular orbitals belonging to the same subspace are imposed to be orthogonal, those belonging to different subspaces are free to overlap. Similar to Hartree-Fock wave function, BLW is also expressed with a Slater determinant. The energy difference between HF wave function and BLW is the stabilization energy due to the intramolecular electron delocalization or the intermolecular charge-transfer effect. In this paper, the applicability of the BLW method is demonstrated by analyzing the rotational barrier in butadiene.

Key words: BUTADIENE, CHARGE TRANSFER, CONJUGATED DOUBLE BOND COMPOUNDS, MOLECULAR ORBITAL THEORY, WAVE FUNCTIONS