From owner-chemistry@ccl.net Sat Dec 28 03:41:01 2024 From: "Akhilesh Sharma sharmaakhil9250 ~ gmail.com" To: CCL Subject: CCL: Yamaguchi's approximate spin projection (AP) method Message-Id: <-55284-241228033936-9845-fV2Neg9m8G14gMJV3uf8/g]-[server.ccl.net> X-Original-From: "Akhilesh Sharma" Date: Sat, 28 Dec 2024 03:39:33 -0500 Sent to CCL by: "Akhilesh Sharma" [sharmaakhil9250###gmail.com] Hello everyone, I am working on a reaction system involving two unpaired electrons on different atoms. I successfully optimized the transition state in the open- shell singlet state, which corresponds to a broken symmetry (BS) solution with S 1. I wish to apply Yamaguchi's approximate spin projection (AP) method and eliminate spin contamination which requires electronic energies of the broken symmetry (BS) as well as high-spin (triplet) states. However, I am encountering difficulties in obtaining the optimized transition state structure (wave function is not converging) in the high-spin (triplet) state where two unpaired electrons are present in the same spin. My question is: Can we utilize single-point electronic energies of the BS and triplet spin states by using the singlet state optimized geometry for the AP method? Or is it necessary to calculate the electronic energies for the BS and triplet spin states at their respective optimized geometries to correctly apply the AP method? Any guidance on how to proceed in this situation would be greatly appreciated. Thank you in advance!