You use your XSEDE username for Atmosphere-launched VMs but there is NO password set -- you cannot use a password to login initially. You have to deploy using an ssh key to login remotely using a terminal-based SSH client or Putty unless you have explicitly set a password via the web shell or web desktop. We recommend starting with this page:
which specifically says this in the red box in the center:
Please note that your XSEDE Portal password is not used for logging into VMs. If you wish to use password authentication to ssh into a VM (not recommended!) you will need to set up a password (refer to Logging in with SSH for information)
and continuing to
in case you need to create and add a key to Atmosphere.