Difference of HOMO of water molecule calculated by HF, MP2, and DFT

From: Pang Siu Kwong <pang()at()iris.chem.cuhk.edu.hk>
Subject: Difference of HOMO of water molecule calculated by HF, MP2, and DFT
Date: Thu, 5 Feb 1998 21:05:32 +0800 (HKT)

 Hello!  I have used the 4-31G for calculation of HOMO of water.  HF,
 MP4(SDQ) and DFT(BP86) are tried.  I found that the results of HF and
 MP4(SDQ) are near the same.  However, the result of DFT is around half of
 those of HF and MP4(SDQ).  Why?
 Thank you for your kindly attention.
 Patrick Pang