Comment on "Ultrathin Mn films on Cu(111) substrates: Frustrated antiferromagnetic order" - art. no. 096401

We have studied collinear and noncollinear magnetic structures of a Mn mono layer on Cu(111) by use of the generalized gradient approximation to the de nsity-functional theory using the full-potential linearized augmented plane -wave method. We found that the inclusion of the gradient correction did no t significantly modify earlier results obtained in the local-density approx imation. Irrespective of the choice of the exchange correlation functional, among the magnetic structures investigated, the minimal energy was found f or a collinear row-wise antiferromagnetic structure. Our findings are at cl ear variance with a recent first-principles study [Phys. Rev. B 61, 12 728 (2000)], which reported that Mn on Cu(111) exhibits a noncollinear ground s tate with magnetic moments forming +/- 120 degrees angles between nearest n eighbors, claiming that this is due to the generalized gradient approximati on essential in these systems. We discuss this point in detail. From our in vestigation of the zero-temperature phase diagram of the Heisenberg model g oing beyond nearest-neighbor interaction, we argue that it is not possible to determine the magnetic ground stare from an investigation of a limited s et of three different magnetic states, but a full investigation of spiral s pin-density waves is required.