Subject: Re: G92/DFT bug? H and LYP

From: [email-masked]
Date: Fri, 3 Feb 1995 15:21:27 -0500 (EST)

>I was using the DFT module of Gaussian 92 (HP-PARisc-HPUX-G92/DFT-RevF.4)
>and came across something that looks like a bug to me: when I try to
>calculate an one-electron system (like the H atom) and use the Lee-Yang-Parr
>functional, my G92 version stops with an IEEE division by zero error.
>I browsed through the code, and sure enough found in the LYP subroutine
>a division by Rho(Beta), which is, in the case of one electron, equal zero.
>I dont have access to the original paper right now, so could someone just
>reassure me that this behavior is definitely an unexpected one, and that
>it doesnt mean that the LYP functional is not valid in the limit of one
>electron or if I only have electrons of one spin species (Gaussian shouldnt 
>abort that ungracefully, anyway...).

This is definitely not the correct behavior -- it's a bug in the code 
I wrote for Gaussian.  Not long after Gaussian obtained the code from me,
I came across the bug and comunicated it to Gaussian, Inc. but apparently
they have not done anything about it.

>A related question is how to get in contact with these Gaussian guys...I
>sent a message to [email-masked] some weeks ago, but havent heard from 
>them back.

>And, could anybody who has access to a DFT implementation (maybe there is
>even a G92 version out there that doesnt show this behavior) that 
>supports Becke 3 parameter XC in connection with the LYP C functional
>calculate the energy for a H radical (with a 6-31G* basis) for me? Pointers
>to papers where this has been done (maybe as a test case for the functional)
>are, of course, also highly welcome.

I could do the calculation for you using the Q-Chem program, which doesn't
have this bug.  You'd need to send me the parameters used in the Becke3LYP
functional, though.  There seems to be a lot of confusion in the literature
over the definition of this method.  To my knowledge, there has never been a 
paper published in which the definition of the Becke3LYP method in G92/DFT
has actually been given, nor does there seem to be any systematic validation
study thoroughly documenting its performance.

I don't know if you're aware, but the method in G92/DFT is not a method of
Becke's.  I have talked with Becke about this, and he is quite skeptical
about the validity of using the particular LYP functional with his
half-and-half approach employing his exchange functional.  So, you may want
to reconsider whether this method is the one you actually want to use.

Best regards,
Benny Johnson
Q-Chem, Inc.
317 Whipple St.
Pittsburgh, PA  15218