Subject: Re: CCL:QUESTIONS:ELECTRON CORRELATION

From: "J. Sichel" <[email-masked]>
Date: Tue, 7 Jul 1998 15:25:17 -0300 (ADT)

On Tue, 7 Jul 1998, E. Lewars wrote:

>             SOME QUESTIONS ABOUT ELECTRON CORRELATION AND THE
>             HARTREE-FOCK METHOD
> 
> 5)  Is there a way to see *intuitively* that the HFM must overestimate
> electron-electron repulsion and underestimate electron kinetic energy?

The exact and HF wave function both obey the virial theorem (Levine
Quantum Chem 4/e p.441)
That is, <V> = -2 <T> and therefore <E> = <T> + <V> = - <T>. 

So since the variational theorem guarantees that E(HF) > E(exact), we must
have T(HF) < T(exact) and V(HF) > V(exact).

John Sichel
Université de Moncton, NB, Canada