Diffusion
The diffusion coefficient in solids can be given in the reference configuration (undeformed configuration, or material frame) or in the deformed configuration (current configuration, or spatial frame). The relation between these reads
here, D is the diffusion coefficient in the reference configuration, and d represents the diffusion coefficient in the deformed configuration. The variables F and J are the deformation gradient and its determinant.
A constant diffusion coefficient D given in material frame implies that its corresponding value in spatial frame, d, depends on the deformation
The frame in which the diffusion coefficient is given can be specified in the Advanced section. From the Frame list select Reference configuration or Deformed configuration to specify a material or spatial diffusion.