(2.2.23) Jones : I agree with Trickey in contribution (2.2.22) and Görling in contribution (2.2.21). The computational effort required in many "real-world" applications is often underestimated -see also Trickey in contribution (3.2.12), concerning other problems of extended systems. A single MD simulation of nanoseconds with a time step of femtoseconds can mean millions (!) of self-consistent DFT calculations of a system with hundreds of atoms. A factor of ten (or even of two) in computer time per time step can mean the difference between completing the calculation and abandoning it.