We argue that the frozen spin-wave energy (either total or internal) is a second-order quantity. The force theorem approximation, whether in the form disscussed, but not used by us, or in the form used by Nicholson and Brown, is accurate only to first order. We agree that they now get agreement with our first-principles calculations and experiment in spite of this.

• Received 3 September 2002

DOI:https://doi.org/10.1103/PhysRevB.67.016402