# Decomposition of elastic constants of a crystalline material

I have performed a calculation the tensor of elastic constants (or stiffness tensor) for a given crystalline material. From there, I calculated various elastic properties, such as Young’s modulus, shear modulus, etc. I have, however, received advice to analyze it by

further decomposing the elastic constant into contributions from the bare terms and phonon relaxation terms

I don't have any more context than that, and I have not been able to identify what these two terms (“bare terms” and “phonon relaxation”) refer to. Does anyone here know?

PS: I don't know if it helps, but the elastic tensor was calculated using quantum chemistry calculations, by measuring the energy of the solid as a function of strain.

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