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We discuss the use of the magnetic force theorem (MFT) using differentreference states upon which the perturbative approach is based. Using adisordered local moment (DLM) state one finds goo d Curie (or Ne\'el)temperatures, and good energetics for planar spin spirals in the 3d magnets Fe,Co (fcc), Mn, Cr. On the other hand the ferromagnetic reference state providesexcellent energetics for small $\theta$ spin spirals in Fe, Co and Ni, and byextension magnon energies under the assumption of adiabacity. However, planarspin spiral energetics and transition temperatures for Ni, Fe, Mn, and Cr showworse agreement. The reasons for this, and for the case of fcc Co whe re bothapproaches work very well are discussed. We further provide an extension of themapping of the quantum problem to include longitudinal fluctuations, anddiscuss the role they will play in magnetic phase transitions. This construction is tested using planar spin spirals where ${\bf q}$ is fixed but themoment is allowed to rel ax. It is demonstrated that results from the magneticforce theorem approach and directly calculated {\it ab initio} values agreevery well

Anab initioeffective Hamiltonian for magnetism including longitudinal spin fluctuations