Editing Functional derivative (section)

==References==
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 | access-date = 2013-10-23
 | archive-url = https://web.archive.org/web/20170217025324/https://www2.ee.washington.edu/techsite/papers/documents/UWEETR-2008-0001.pdf
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 | chapter = Section 2.3 – Functional derivatives
 | pages = [https://archive.org/details/fieldquantizatio0000grei/page/36 36–38]
 | chapter-url = https://archive.org/details/fieldquantizatio0000grei/page/36
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*{{cite book |first1=R. G.|last1=Parr|first2=W.|last2=Yang| title = Density-Functional Theory of Atoms and Molecules | chapter = Appendix A, Functionals | pages = 246–254 | publisher = Oxford University Press | year = 1989 |location=New York| url = https://books.google.com/books?id=mGOpScSIwU4C&q=Density-Functional+Theory+of+Atoms+and+Molecules | isbn = 978-0195042795}}