From chemistry-request@ccl.net Sun Aug 2 09:08:46 1992 Date: Sat, 1 Aug 92 10:52:52 EDT From: m10!frisch@uunet.UU.NET (Michael Frisch) Subject: CI wavefunction norm in Gaussian To: chemistry@ccl.net Status: R Dear fellow netters, I am running CI(SD) calculations using G90, and I am trying to extract the coefficient of the HF configuration. The manual says (page 165) that "Norm(A1) - 1 gives a measure of the correlation correction to the wavefunction." But what exactly is the coefficient for the HF configuration? My guess is that it is given by 1/Norm(A1), but I am not sure. Any comments? Thank you, Gernot Frenking frenking@dmrhrz11.bitnet Your guess is correct. This is one of the most commonly asked questions, and the G92 manual has the equation for Norm(A) in an attempt to make the relationship clearer. The wavefunction is stored in intermediate normalization. That is: Psi(CISD) = Psi(0) + Sum(ia) Tia Psi(i-->a) + Sum (ijab) Tijab Psi(ij-->ab) Where Psi(0) is the Hartree-Fock determinant and has a coefficient of 1 (that's what intermediate normalization means). Norm(A) is the factor by which to divide the wavefunction as given above to fully normalize it. Thus Norm(A) = Sqrt (1 + Sum(ia) Tia*Tia + Sum(ijab) Tijab*Tijab) The coefficient of the Hartree-Fock determinant in the fully normalized wavefunction is then 1/Norm(A), the coefficient of singly excited determinant Psi(i-->a) is Tia/Norm(A), etc. Another pitfall to be careful of is that the sum over the doubly-excited determinants is really restricted to the unique determinants. It is really Sum(iab ijab all alpha spin) + Sum(all ijab) Psi(ij-->ab i,a alpha j,b beta) + Sum(iab ijab all beta spin) For closed shell, the all beta coefficients are equal to the all alpha coefficients and if you request that the coefficients be printed (using IOP(9/28=N) to get coefficients larger than 10^-N or IOP(9/28=-1) to get all coefficients) only the alpha-alpha and alpha-beta coefficients will be printed. Mike Frisch ------- --- Administrivia: This message is automatically appended by the mail exploder. CHEMISTRY@ccl.net --- everybody; CHEMISTRY-REQUEST@ccl.net --- coordinator only OSCPOST@ccl.net : send something from chemistry; FTP: www.ccl.net ---