The　decomposition　of　methanol　on　clean　and　oxygen-precovered　CuCl(1　1　1)　surface　have　been　studied　with　the　method　of　density　functional　theory-generalized　gradient　approximation　(DFT-GGA)　and　the　periodic　slab　models.　The　effects　of　different　methanol　coverages　up　to　one　monolayer　are　investigated.　The　activation　of　the　O-H　bond　of　methanol　to　form　the　methoxide　intermediate,　the　activation　of　the　C-H　bond　to　form　the　hydroxymethyl　intermediate　and　the　activation　of　the　C-O　bond　to　form　methyl　are　examined.　These　intermediates　can　subsequently　react　to　form　methoxide,　hydroxymethyl,　methyl,　formaldehyde,　formyl,　and　finally　CO　on　the　surface.　The　chemisorption　energies　of　CH3OH,　CH3O,　H2COH,　CH3,　H2CO,　HCO,　OH　and　CO　at　their　most　favorable　adsorption　sites　are　predicted　to　be　-57.9,　-235.3,　-172.9,　-170.5,　-67.8,　-192.4,　-309.5　and　-105.7　kJ/mol,　respectively.　We　also　confirm　that　the　O-H　bond-breaking　paths　have　lower　energy　barrier,　compared　to　the　C-O　and　C-H　bond-breaking　paths.　However,　these　reactions　need　a　lower　energy　barrier　when　precovered　oxygen　atoms　participate　in　these　reactions.　©　2008　Elsevier　B.V.　All　rights　reserved.