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Ministerio de Ciencia e InnovaciÃ³n (Espanya)
Ministerio de EducaciÃ³n y Ciencia (Espanya) Generalitat de Catalunya. AgÃ¨ncia de GestiÃ³ dâ€™Ajuts Universitaris i de Recerca 

RuizBarragÃ¡n, Sergi
Robb, Michael A. Blancafort San JosÃ©, LluÃs 

An algorithm for conical intersection optimization based on a double NewtonRaphson step (DNR) has been implemented and tested in 11 cases using CASSCF as the electronic structure method. The optimization is carried out in redundant coordinates, and the steps are the sum of two independent NewtonRaphson steps. The first step is carried out to reach the energy degeneracy and uses the gradient of the energy difference between the crossing states and the socalled branching space Hessian. The second step minimizes the energy in the intersection space and uses the projected excited state gradient and the intersection space Hessian. The branching and intersection space Hessians are obtained with a BroydenFletcherGoldfarbShanno update from the gradient difference and projected excited state gradients, respectively. In some cases, mixing of the quasidegenerate states near the seam causes changes in the direction of the gradient difference vector and induces a loss of the degeneracy. This behavior is avoided switching to a composed step (CS) algorithm [Sicilia et al. J. Chem. Theory Comput.2008, 4, 27], i.e., a hybrid DNRCS implementation. Compared to the composed gradient (CG) [Bearpark et al. Chem. Phys. Lett.1994, 223, 269] and hybrid CGCS algorithms, the DNRCS algorithm reaches the MECI in 30% and 15% less steps, respectively. The improvement occurs mostly because the approach to the seam is more efficient, and a degeneracy threshold of 0.001 hartree is reached at lower energies than in the CG and CGCS cases This work has been supported by grants CTQ200806696 and CTQ201126573 from the Spanish Ministerio de Ciencia e Innovacion (MICINN) and Ministerio de Economia y Competividad (MINECO), respectively, SGR0528 from the Catalan Agencia de Gestio dâ€™Ajuts Universitaris i de Recerca (AGAUR), UNGI084E003 from MICINN and the European Fund for Regional Development, and the Xarxa de Referencia en Quimica Teorica i Computacional de Catalunya from AGAUR S.R.B. thanks the MICINN for grant BES2009029177 

http://hdl.handle.net/2072/296730  
eng  
American Chemical Society (ACS)  
Tots els drets reservats  
OptimitzaciÃ³ matemÃ tica
Mathematical optimization QuÃmica quÃ ntica Quantum chemistry QuÃmica de lâ€™estat excitat Excited state chemistry 

Conical intersection optimization based on a double NewtonRaphson algorithm using composed steps  
info:eurepo/semantics/article  
Recercat 