We have performed a series of highly accurate calculations between CO2and the 20 naturally occurring amino acids for the investigation of the attractive noncovalent interactions. Different nucleophilic groups present in the amino acid structures were considered (α‐NH2, COOH, side groups), and the stronger binding sites were identified. A database of accurate reference interactions energies was compiled as computed by explicitly‐correlated coupled‐cluster singles‐and‐doubles, together with perturbative triples extrapolated to the complete‐basis‐set limit. The CCSD(F12)(T)/CBS reference values were used for comparing a variety of popular density functionals with different basis sets. Our results show that most density functionals with the triple‐zeta basis set def2‐TZVPP align with the CCSD(F12)(T)/CBS reference values, but errors range from 0.1 kcal/mol up to 1.0 kcal/mol.
In multichromophore systems, characterization of electronic structure requires characterization of exciplexes, electron‐hole pairs delocalized over multiple molecules. Computing exciplex binding energy requires an accurate description of both the noncovalent interactions between the chromophores and their excited electronic states. The critical role of basis set selection for accurate description of noncovalent interactions is well known, but for some of the most accurate excited‐state methods, basis set dependence is incompletely understood. In this work, the impact of basis set size and diffuseness on CASSCF/NEVPT2 binding energies is determined for three systems in their lowest singlet excited states: the benzene excimer, the
- NSF-PAR ID:
- 10078144
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- International Journal of Quantum Chemistry
- Volume:
- 119
- Issue:
- 5
- ISSN:
- 0020-7608
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract The enantiomers of eight axially chiral biaryls were separated by chiral HPLC. On‐column enantiomerization of 1‐(
o ‐tolyl)naphthalene and 2‐cyclohexyl‐2′‐dimethylaminobiphenyl was observed between 10 °C and 35 °C, generating characteristic HPLC elution profiles with a plateau between the resolved enantiomer peaks. Computer simulation of the experimentally obtained chromatograms allowed determination of the Gibbs free energies of activation, ΔG ≠, as 93.2 kJ/mol and 88.4 kJ/mol, respectively. -
more » « less
The Grimme‐D3 semi‐empirical dispersion energy correction has been implemented for the original effective fragment potential for water (EFP1), and for systems that contain water molecules described by both correlated
ab initio quantum mechanical (QM) molecules and EFP1. Binding energies obtained with these EFP1‐D and QM/EFP1‐D methods were tested using 27 benchmark species, including neutral, protonated, deprotonated, and auto‐ionized water clusters and nine solute–water binary complexes. The EFP1‐D and QM/EFP1‐D binding energies are compared with those obtained using fully QM methods: second‐order perturbation theory, and coupled cluster theory, CCSD(T), at the complete basis set (CBS) limit. The results show that the EFP1‐D and QM/EFP1‐D binding energies are in good agreement with CCSD(T)/CBS binding energies with a mean absolute error of 5.9 kcal/mol for water clusters and 0.8 kcal/mol for solute–water binary complexes. © 2018 Wiley Periodicals, Inc. -
Insight into the Binding of Argon to Cyclic Water Clusters from Symmetry-Adapted Perturbation Theorymore » « less
This work systematically examines the interactions between a single argon atom and the edges and faces of cyclic H2O clusters containing three–five water molecules (Ar(H2O)n=3–5). Full geometry optimizations and subsequent harmonic vibrational frequency computations were performed using MP2 with a triple-ζ correlation consistent basis set augmented with diffuse functions on the heavy atoms (cc-pVTZ for H and aug-cc-pVTZ for O and Ar; denoted as haTZ). Optimized structures and harmonic vibrational frequencies were also obtained with the two-body–many-body (2b:Mb) and three-body–many-body (3b:Mb) techniques; here, high-level CCSD(T) computations capture up through the two-body or three-body contributions from the many-body expansion, respectively, while less demanding MP2 computations recover all higher-order contributions. Five unique stationary points have been identified in which Ar binds to the cyclic water trimer, along with four for (H2O)4 and three for (H2O)5. To the best of our knowledge, eleven of these twelve structures have been characterized here for the first time. Ar consistently binds more strongly to the faces than the edges of the cyclic (H2O)n clusters, by as much as a factor of two. The 3b:Mb electronic energies computed with the haTZ basis set indicate that Ar binds to the faces of the water clusters by at least 3 kJ mol−1 and by nearly 6 kJ mol−1 for one Ar(H2O)5 complex. An analysis of the interaction energies for the different binding motifs based on symmetry-adapted perturbation theory (SAPT) indicates that dispersion interactions are primarily responsible for the observed trends. The binding of a single Ar atom to a face of these cyclic water clusters can induce perturbations to the harmonic vibrational frequencies on the order of 5 cm−1 for some hydrogen-bonded OH stretching frequencies.
-
more » « less
Abstract Emissive properties for the cationic exciplex (A+*/D→A.D.+) of an isoquinolinium cation tethered to a substituted arene (
1+ ) are strongly affected by hydrogen bonding solvents. At equal dielectric constant (ϵ ), the ground‐to‐excited state energy gaps (ΔG ) and solvent reorganization energies (λ s) decrease from nitriles to aliphatic alcohols. The corresponding decrease from aliphatic alcohols to high hydrogen bond acidity solvents is ∼3 times larger. The exciplex decay (k Ex), largely determined by unfolding of the exciplex to a stretched conformer, changes in a complex way depending on the strength of the hydrogen bond ability of these solvents. In contrast, the electronic couplings between the exciplex ground, excited, and charge transfer states do not show a solvent functionality dependence.
