Optimization of force constants with an Urey-Bradley force field avoiding normal mode crossings.
We present a method that simplifies the refinement of force constants in normal mode calculations and makes the results more reliable. The method avoids normal mode crossings by constraining the force constants during refinement. It was tested with pyrrole, imidazole, benzene, pyridine, pyrimidine, aniline and adenine using a Urey-Bradley force field. The global error of the frequency fit for these molecules was 0.61%. The method reproduced with fewer parameters the accuracy of similar calculations of the single ring aromatic compounds. It improved the accuracy and isotopic shifts of previous empirical calculations of adenine by 40%. The C-C and C-N stretchings differed by less than 7% from the values of force constant-bond length empirical relations.
Vivoni
A
A
Department of Biology, Chemistry and Environmental Sciences, Inter American University, San Germán, Puerto Rico, USA. avivoni@alpha.sg.inter.edu
Birke
R
R
Lombardi
J
J
D000225:Adenine / Q000737:chemistry; D000814:Aniline Compounds / Q000737:chemistry; D001554:Benzene / Q000737:chemistry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D006571:Heterocyclic Compounds / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry; D008956:Models, Chemical; D015394:Molecular Structure; D009930:Organic Chemicals / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry; D011743:Pyrimidines / Q000737:chemistry; D011758:Pyrroles / Q000737:chemistry; D012984:Software
D000814:Aniline Compounds; D006571:Heterocyclic Compounds; D007093:Imidazoles; D009930:Organic Chemicals; D011725:Pyridines; D011743:Pyrimidines; D011758:Pyrroles; C029899:imidazole; D001554:Benzene; D000225:Adenine; C023650:aniline