Why can off-diagonal cubic force constants be non-zero in VPT2?

So in the VPT2 treatment I get how we can expand the potential V along a normal coordinate q_i as: V = 1/2 k_ii * q_i^2 + 1/6 k_iii * q_i^3 + 1/24 k_iiii * q_i^4 and we get non-zero elements for...

23 May 2024 7,901 0 View