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　CH　3　OH,　CH　3　O,　H　2　COH,　CH　3　,　H　2　CO,　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.