This review explains the relationship between density functional theory and strongly correlated models using the simplest possible example, the two-site Hubbard model. The relationship to traditional quantum chemistry is included. Even in this elementary example, where the exact ground-state energy and site occupations can be found analytically, there is much to be explained in terms of the und...

To draw causal conclusions about the efficacy of a psychological intervention, researchers must compare the treatment condition with a control group that accounts for improvements caused by factors other than the treatment. Using an active control helps to control for the possibility that improvement by the experimental group resulted from a placebo effect. Although active control groups are su...

The question of how density functional theory (DFT) compares with Hartree-Fock (HF) for the computation of momentum-space properties is addressed in relation to systems for which (near) exact Kohn-Sham (KS) and HF one-electron matrices are known. This makes it possible to objectively compare HF and exact KS and hence to assess the potential of DFT for momentum-space studies. The systems conside...

There is an obvious need for a critical discussion of the concepts 'placebo' and 'placebo effect'. In a recent paper on the use of placebos in clinical medicine, Gold and Lichtenberg note the conceptual difficulties but use the terminology in a confused way throughout their paper. In our response, we demonstrate these problems with a few examples from their paper.

This article is a rebuttal to Kevin Smith's 'Against Homeopathy,' which was posted on 14 February 2011.(1) It contends that his argument rests entirely on the assumption that homeopathic remedies are nothing but placebos. His argumentation is good, but his assumption is false. Evidence is presented to show that the Law of Similars is plausible and that ultradilute remedies do indeed have biolog...

The main current application of placebo is in clinical research. The term placebo effect refers to diverse non-specific, desired or non-desired effects of substances or procedures and interactions between patient and therapist. Unpredictability of the placebo effect necessitates placebo-controlled designs for most trials. Therapeutic and diagnostic use of placebo is ethically acceptable only in...