When you perform a structural optimisation on a crystal system is it considered a Lattice Statics or Lattice Dynamics calculation?
As I understand it, phonon calculations and elastic modulus calculations, for example, are Lattice Dynamics, as they are modelling atom movement, but I’m not sure about structural optimisation. The atoms do move throughout the process, but is it right to say the calculations don’t take into account any movement, thus making it a Lattice Statics method?
I guess it’s all a bit semantic as to what you call things - it’s safer to safe that the structure is optimised and the phonons computed. Lattice dynamics is arguably strictly about the phonons since the motion in the dynamics is the vibration. Elastic constants are linked to the acoustic limit of the phonons and so could be considered to be part of this, even though there is no dynamics. Optimisation is a pre-requiste for computing phonons (meaningfully) and so could also be place under a lattice dynamics calculation, though it’s static in that the atoms have no kinetic energy (though in reality if a structure was relaxing then they would gain kinetic energy). So I’d probably use lattice dynamics to refer to optimisation + phonon calculation, and just optimisation for an internal energy calculation, but the boundaries are blurred.