# Isotropic crystal and energy band

1. ### hokhani

300
Since all the directions are equivalent in an isotropic crystal, can we deduce that the energy band is exactly spherical?

2. ### DrDu

4,161
The problem is that there are no isotropic crystals. Even cubic crystals are only symmetric with respect to four and threefold rotations about some special axes. However this is sufficient to render second order (but not higher order) tensors isotropic.

3. ### hokhani

300
Do you mean that using the isotropic approximation we in fact disregard the crystal?

4. ### DrDu

4,161
Yes, indeed.

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