  Isomorphs are curves in the thermodynamic phase diagram along which structure
and dynamics are invariant to a good approximation. There are two main ways to
trace out isomorphs, the configurational-adiabat method and the
direct-isomorph-check method. Recently a new method based on the scaling
properties of forces was introduced and shown to work very well for atomic
systems [T. B. Schroder, Phys. Rev. Lett. 129, 245501 (2022)]. A unique feature
of this method is that it only requires a single equilibrium configuration for
tracing out an isomorph. We here test generalizations of this method to
molecular systems and compare to simulations of three simple molecular models:
the asymmetric dumbbell model of two Lennard-Jones spheres, the symmetric
inverse-power-law dumbbell model, and the Lewis-Wahnstr\"om o-terphenyl model.
We introduce and test two force-based and one torque-based methods, all of
which require just a single configuration for tracing out an isomorph. Overall,
the method based on requiring invariant center-of-mass reduced forces works
best.
