From owner-chemistry@ccl.net Thu Aug 4 14:54:00 2016 From: "Yuanhe Li liyuanhe211^_^163.com" To: CCL Subject: CCL:G: Calculating interaction energy/bond energy between atoms in mole:G Message-Id: <-52355-160804141333-19457-q5o+mdttTnvL+LKrWnLoEg!A!server.ccl.net> X-Original-From: "Yuanhe Li" Date: Thu, 4 Aug 2016 14:13:32 -0400 Sent to CCL by: "Yuanhe Li" [liyuanhe211_._163.com] Counterpoise is a correction for BSSE error in (weak) intermolecular interaction energy. What you want is probably irrelevant to it. If you mean by cutting the 4 bonds:"1-4,5-28,3-8,11-17" simultaneously, splitting the molecule in to two (tetra-radical?) fragment, and you want the interaction between those (roughly equal to the sum of the bond energies). You can just calculate the two fragments A, B, the molecule AB; get the difference of electronic energy. This is a (very) strong interaction, thus no counterpoise is required. However, I can't see why this is meaningful, and the fragment electronic structure might be tricky. If you mean you want the bond energy for each of the 4 bonds, be aware that the bond energy of a bond inside a ring is ambiguous. You have the liberty to design reasonable processes to represent it, like rotating one side of the ring away > from the bonding position, then calculate the singlet biradical. Also one should try to cancel any artificial interaction during the process like steric repulsion. Or you can calculate the Laplacian bond order, which is well correlated with bond energy in organic systems. (Laplacian bond order cannot be calculated by Gaussian, try Multiwfn: https://multiwfn.codeplex.com/) Sent to CCL by: "Nikhil Maroli" [scinikhil[#]gmail.com] Dear all, im new to gaussian, i wanted to calculate the interaction energy between the atoms in the molecules (image : https://drive.google.com/file/d/0BxaQk_pcR9vibDhhTzFQQmZjOWM/view? usp=sharing) I know I can use counterpoise method by making it two fragments ,but how it is possible for finding interaction energy between the 1-4,5-28,3-8,11-17. how I make fragments? Any suggestion will be helpful