It will depend on the version that you're using. MAM3 is the default in CAM5. MAM7 is present in most recent versions, but it is not "supported" (use at your own risk), and I don't think that we have released a compset so far. (I don't recall what's available in which version off the top of my head, but you can look at compsets in the documentation or in the output of "create_newcase -list compsets".)If there's not a compset, you can pick an existing compset and change the chemistry by modifying the variable "CAM_CONFIG_OPTS" to add "-chem trop_mam7", but I have never used MAM7, and I can't say if it works well (or at all) with any specific version and configuration of CAM5.