Showing papers by "Kwang S. Kim published in 1995"
TL;DR: Using extensive ab initio calculations including electron correlation, the authors have studied structures, thermodynamic quantities, and spectra of hydrated sodium ions [Na(H2O)+n (n=1-6) and found that the enthalpy effect was the dominant factor to determine the primary hydration number of Na+ in aqueous solution.
Abstract: Using extensive ab initio calculations including electron correlation, we have studied structures, thermodynamic quantities, and spectra of hydrated sodium ions [Na(H2O)+n (n=1–6)] Various configurations were investigated to find the stable structures of the clusters The vibrational frequency shifts depending on the number of water molecules were investigated along with the frequency characteristics depending on the presence/absence of outer‐shell water molecules The thermodynamic quantities of the stable structures were compared with experimental data available Entropy‐driven structures for n=5 and particularly for n=6 are noted in the calculations, which can explain the peculiar experimental thermal energies On the other hand, the enthalpy effect to maximize the number of hydrogen bonds of the clusters with the surrounding water molecules seems to be the dominant factor to determine the primary hydration number of Na+ in aqueous solution The nonadditive interactions in the clusters are found to be
155 citations
TL;DR: In this paper, the most stable structure and binding energies of benzene with ammonium cations were reported using ab initio calculations with electron correlation included, and the calculated binding energies were in good agreement with experiment two types of NH-α and CH-α π interactions are responsible for the binding.
100 citations
TL;DR: In this article, various levels of ab initio theory using various basis sets have been tested for the energy, structure, and harmonic vibrational frequencies of the water monomer, and the results showed that at the Hartree-Fock (HF) level frequency shifts in the dimer relative to the monomer were underestimated, while at the MP2 level these are overestimated.
Abstract: Various levels of ab initio theory using various basis sets have been tested for the energy, structure, and harmonic vibrational frequencies of the water monomer. The level of the single, double, and perturbative triple excitation coupled‐cluster method [CCSD(T)] using a large basis set (O:13s,8p,4d,2f/ H:8s,4p,2d) reproduced the experimental harmonic vibrational frequencies of the water monomer within the error of 0.6 cm−1. Other calculational methods seem to have inherent errors in predicting vibrational frequencies. Even with the above large basis set significant differences between symmetric and asymmetric stretching frequencies were found at various levels of calculational method including the commonly used Moller–Plesset 2nd (MP2) and 4th (MP4) order perturbation theories. The harmonic vibrational frequencies and force constants of the water dimer at various levels of ab initio theory have also been studied, and their shifts in the dimer relative to the monomer are discussed. At the Hartree–Fock (HF) level frequency shifts in the dimer relative to the monomer as well as hydrogen bonding strength in the dimer are underestimated, while at the MP2 level these are overestimated. The values at the CCSD(T) level seem to be reliable.
77 citations
46 citations
41 citations
TL;DR: The conformational energies of ligands for carboxypeptidase A are examined using ab initio calculations and the energetic preference of the unbound ligand conformers which arises from the stereoelectronic effect appears to play a significant role in determining the bound ligands conformations.
Abstract: Because of the complexity involved in binding of a ligand to an enzyme the conformational preference of the bound ligand has not been well understood yet. We have examined the conformational energies of ligands for carboxypeptidase A using ab initio calculations. Considering the large stereoelectronic effect of 4∼5 kcal/mol, the energetic preference of the unbound ligand conformers which arises from the stereoelectronic effect appears to play a significant role in determining the bound ligand conformations.
1 citations