# CCL:G: Tozer's diagnostic test in Gaussian

*From*: "J. Phoenix"
<himphoenixCCL.**.gmail.com>
*Subject*: CCL:G: Tozer's diagnostic test in Gaussian
*Date*: Tue, 15 Jul 2014 10:09:16 -0400

Sent to CCL by: "J. Phoenix" [himphoenixCCL_._gmail.com]
Dear CCLs,
I am trying to compute the Tozer's lambda parameter that relates the spatial
overlap between orbitals in a certain excitation using TDDFT calculations (JCP,
128, 044118 (2008)). The procedure I am following is to extract the overlap
matrix of AOs in the Gaussian output and then compute for each MO pair:
<Psi_1|Psi_2> = sum_i sum_j c_1_i c_2_j <X_i|X_j>, using the MO
coefficients. When coefficients are taken with their sign, I get an overlap of
one between the same MO, and zero between different MOs. However, when I use the
absolute value of the coefficients to compute the inner product of the moduli,
overlaps larger than 1 are obtained in some cases.
Is there anything wrong in my procedure for computing the inner product of the
moduli of two orbitals or is not expected to be a value between 0 and 1?
Thanks in advance,
J.