Description:

I, the author of the article, could not find any accessible text explaining how formulas like the general definition of the functional derivative and the Taylor series of a functional are derived. Most texts claiming to be introductory, cite the appendix A of Parr and Yang. This appendix is not an introduction to functional derivatives and while the formulas written are correct, the conclusions drawn and assumptions made are not at all obvious. I have taken the time to write a functional derivatives for dummies guide for those who are interested in learning about functional derivatives and for those who need it for academic purposes. They are used all through Quantum field theory and Density functional theory and hence are essential tools for the theoretical chemist and physicist. I hope that you find the article useful. If you do, please email me at: Nicholas.Fisk@kcl.ac.uk. I will also be more than happy to answer any questions.