Contrast theory three dimensions

The density functional theoiy (DFT) was mentioned previously in Chapter 4, and the Thomas-Fermi method can also be viewed as a special case of DFT. DFT has become very popular over the last 20 years or so. The reasons are obvious — it scales as where N is the number of electrons—by contrast to standard ab initio Hartree-Fock theory, which scales as N, and the results are more accurate (not to mention accurate ab initio theories, which scale as N ). Furthermore the DFT theory operates in three dimensions (x, y, z) in which the electron density is defined—no matter how many electrons are involved. DFT theory has been reviewed and described in numerous books and review articles see, for instance, [212]. We shall therefore only give a brief presentation of it here. 

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