MULTI-COMPONENT MOLECULAR ORBITAL THEORY -- CONTENTS -- PREFACE -- INTRODUCTION -- MULTI-COMPONENT MOLECULAR ORBITAL METHODS -- 2-1. PIONEERING WORKS BY I. L. THOMAS -- 2-2. MULTI-COMPONENT MOLECULAR ORBITAL METHODS -- 2-3. OTHER GROUP'S APPROACH -- APPLICATION OF THE MULTI-COMPONENT METHODS -- 3-1. APPLICATION OF THE FULL-CI MC_MO TO THE POSITRON-MOLECULE COMPLEXES WITH FVMO PROCEDURE -- 3-1-1. H- system -- 3-1-2. [H- -- e+(1s)] -- 3-1-3. [H- -- e+(2p)] -- 3-1-4. Optimized basis functions -- 3-1-5. Positron-molecular system [OH- -- e+] -- 3-1-6. Comparison of optimum basis function and energies in Li-, [Li- -- e+], LiH, and LiD systems. -- 3-2. AN ANALYSIS OF THE ISOTOPE EFFECTS ON HYDROGEN MOLECULES BY USING FULL-CI MC_MO CALCULATION -- 3-2-1. Basis set dependence of H2 molecule -- 3-2-2. Isotope effect of H2, D2, T2, and μ2 molecules -- 3-3. AN ANALYSIS OF THE H/D ISOTOPE EFFECT ON PORPHINE AND PORPHYCENE MOLECULES REVEALED BY THE MC_DFT METHOD -- 3-3-1. Optimized geometries of HH-molecules -- 3-3-2. Geometric isotope effect on DD-molecules -- 3-3-3. Symmetric breaking down in HD-molecules -- CONCLUSIONS -- REFERENCES -- Untitled.