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SCC‐DFTB energy barriers for single and double proton transfer processes in the model molecular systems malonaldehyde and porphycene
Author(s) -
Walewski Ł.,
Krachtus D.,
Fischer S.,
Smith J. C.,
Bała P.,
Lesyng B.
Publication year - 2005
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.20810
Subject(s) - intramolecular force , ab initio , chemistry , structural isomer , proton , computational chemistry , potential energy , ab initio quantum chemistry methods , molecule , stereochemistry , atomic physics , organic chemistry , physics , quantum mechanics
Self‐consistent charge–density functional tight‐binding SCC‐DFTB is a computationally efficient method applicable to large (bio)molecular systems in which (bio)chemical reactions may occur. Among these reactions are proton transfer processes. This method, along with more advanced ab initio techniques, is applied in this study to compute intramolecular barriers for single and double proton transfer processes in the model systems, malonaldehyde and porphycene, respectively. SCC‐DFTB is compared with experimental data and higher‐level ab initio calculations. For malonaldehyde, the SCC‐DFTB barrier height is 3.1 kcal/mol in vacuo and 4.2 kcal/mol in water solution. In the case of porphycene, the minimum energy pathways for double intramolecular proton transfer were determined using the conjugate peak refinement (CPR) method. Six isomers of porphycene were ordered according to energy. The only energetically allowed pathway was found to connect two symmetrical trans states via an unstable cis‐A isomer. The SCC‐DFTB barrier heights are 11.1 kcal/mol for the trans‐cis‐A process, and 7.4 kcal/mol for the reverse cis‐A‐trans one with the energy difference of 3.7 kcal/mol between the trans‐ and cis‐A states. The method provides satisfactory energy results when compared with reference ab initio and experimental data. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006