TY - JOUR
T1 - Performance of M06, M06-2X, and M06-HF density functionals for conformationally flexible anionic clusters
T2 - M06 functionals perform better than B3LYP for a model system with dispersion and ionic hydrogen-bonding interactions
AU - Harvey, A.J.A.
AU - Sen, A.
AU - Dessent, Caroline Elizabeth Helen
AU - Walker, M
PY - 2013/11/27
Y1 - 2013/11/27
N2 - We present a comparative assessment of the performance of the M06 suite of density functionals (M06, M06-2X, and M06-HF) against an MP2 benchmark for calculating the relative energies and geometric structures of the Cl ·arginine and Br·arginine halide ion-amino acid clusters. Additional results are presented for the popular B3LYP density functional. The Cl·arginine and Br ·arginine complexes are important prototypes for the phenomenon of anion-induced zwitterion formation. Results are presented for the canonical (noncharge separated) and zwitterionic (charge separated) tautomers of the clusters, as well as the numerous conformational isomers of the clusters. We find that all of the M06 functions perform well in terms of predicting the general trends in the conformer relative energies and identifying the global minimum conformer. This is in contrast to the B3LYP functional, which performed significantly less well for the canonical tautomers of the clusters where dispersion interactions contribute more significantly to the conformer energetics. We find that the M06 functional gave the lowest mean unsigned error for the relative energies of the canonical conformers (2.10 and 2.36 kJ/mol for Br·arginine and Cl·arginine), while M06-2X gave the lowest mean unsigned error for the zwitterionic conformers (0.85 and 1.23 kJ/mol for Br·arginine and Cl ·arginine), thus providing insight into the types of physical systems where each of these functionals should perform best.
AB - We present a comparative assessment of the performance of the M06 suite of density functionals (M06, M06-2X, and M06-HF) against an MP2 benchmark for calculating the relative energies and geometric structures of the Cl ·arginine and Br·arginine halide ion-amino acid clusters. Additional results are presented for the popular B3LYP density functional. The Cl·arginine and Br ·arginine complexes are important prototypes for the phenomenon of anion-induced zwitterion formation. Results are presented for the canonical (noncharge separated) and zwitterionic (charge separated) tautomers of the clusters, as well as the numerous conformational isomers of the clusters. We find that all of the M06 functions perform well in terms of predicting the general trends in the conformer relative energies and identifying the global minimum conformer. This is in contrast to the B3LYP functional, which performed significantly less well for the canonical tautomers of the clusters where dispersion interactions contribute more significantly to the conformer energetics. We find that the M06 functional gave the lowest mean unsigned error for the relative energies of the canonical conformers (2.10 and 2.36 kJ/mol for Br·arginine and Cl·arginine), while M06-2X gave the lowest mean unsigned error for the zwitterionic conformers (0.85 and 1.23 kJ/mol for Br·arginine and Cl ·arginine), thus providing insight into the types of physical systems where each of these functionals should perform best.
UR - http://www.scopus.com/inward/record.url?scp=84889066017&partnerID=8YFLogxK
U2 - 10.1021/jp408166m
DO - 10.1021/jp408166m
M3 - Article
AN - SCOPUS:84889066017
SN - 1089-5639
VL - 117
SP - 12590
EP - 12600
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 47
ER -