In multifrequency atomic force microscopy higher eigenmodes are externally
excited to enhance resolution and contrast while simultaneously increasing the
number of experimental observables with the use of gentle forces. Here, the
implications of externally exciting multiple frequencies are discussed in terms
of cantilever anharmonicity, fundamental period and the onset of subharmonic
and superharmonic components. Cantilever anharmonicity is shown to affect and
control both the observables, that is, the monitored amplitudes and phases, and
the main expressions quantified via these observables, that is, the virial and
energy transfer expressions which form the basis of the theory
