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Ghost states

The fully separable form of pseudopotential would possess artificial ghost states [17], which is one of serious problems in the separable form, while multiple projectors proposed by Blöchl [8] is highly effective to avoid the existence of ghost states. To check it, a keyword, ghost.check, is provided. Although the keyword is useful to find the ghost states, however, it should be noted that a complete check to detect the ghost states is difficult.