Subject: Re: CCL:gradients of overlap integrals

From: [email-masked]
Date: Thu, 30 Jul 1998 19:12:06 +0200 (DFT)

> We need to calculate the gradient of an overlap integral
> between tight-binding basis functions. 
> i.e. we need
> d/dx <psi_a | psi_b>  

You may take a look at 
F.X.Gadea, M.Pelissier, J. Chem. Phys 96 (1990) 545
They use finite increments, i.e.
d/dx<psi_a | psi_b> \approx (1/dx)(<psi_a | psi_b(x+dx)> - <psi_a | psi_b(x) >)
in order to compute radial coupling terms between functions.
Recently I've been working on partially analytical computation of these terms;
computing d(psi_b)/dx is quite straightforward when psi_b is a gaussian 
function. 

Hope it helps, 
JM
-- 
LIFE IS SO UNCERTAIN - EAT DESSERT FIRST 
                                 
Juan Miguel Bocanegra Moron (mailto:[email-masked])
Grup de Cinetica i Dinamica de Reaccions Elementals     
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