Showing papers by "Enrico Clementi published in 1982"
IBM1
TL;DR: A new type of basis set - called geometrical - is proposed designed mainly for improving large-molecule computations but it is tested with an accuracte computation for H2O.
76 citations
IBM1
TL;DR: It is determined that the counterions themselves conform to two helical structures intertwined with the two strands, and a model for base‐pair recognition based on the above findings is proposed.
Abstract: We report on a computer experiment in which, using Monte Carlo techniques, we considered a three-turn (30-base-pairs) B-DNA fragment as a solute and a set of 1200 water molecules and 60 sodium counterions (at a temperature of 300 K) as a solvent. From a statistical analysis of the Monte Carlo simulation (applied to the water molecules and counterions in the B-DNA field), we determined that the counterions themselves conform to two helical structures intertwined with the two strands. The strutures of the water molecules solvating both counterion helices and the two B-DNA strands are fully analyzed and described in detail. A model for base-pair recognition based on the above findings is proposed. Aspects of the unwinding mechanism are discussed.
57 citations
IBM1
TL;DR: Monte Carlo simulations for a methanol molecule enclosed in a cluster of 198 water molecules are presented in this paper, where the water structure near the methyl group is similar to that reported for methane.
52 citations
IBM1
TL;DR: In this article, the Monte Carlo method using quantum-mechanically derived potentials was used to analyze 17 different computer experiments, where a three-turn B-DNA double helix fragment interacted with a variable number of water molecules (from 60 to 1200), with a varying number of sodium ions (from 30 to 63), at one or more temperatures (280, 300, 320 K).
Abstract: Seventeen different computer experiments are presented and analyzed. In each experiment a three-turn B-DNA double helix fragment interacts with a variable number of water molecules (from 60 to 1200), with a variable number of sodium ions (from 30 to 63), at one or more temperatures (280, 300, 320 K). The experiments are performed with the Monte Carlo method using quantum-mechanically derived potentials. In the analysis of the experiments we partition the water molecules (and the corresponding interactions) as being either bound or in the first solvation shell or in the groove regions relative to DNA; for the former two cases, the number of water molecules and the water interaction energy are reported for selected atoms or groups of atoms. The entire study is condensed into eight tables. The use of these tables is exemplified by considering, in detail, some of the trends emerging from these experiments. The analyses are complemented by graphical representations presented either to elucidate the very complex pattern of hydrogen bonded water molecules, or to show the statistical distributions of the oxygen and hydrogen atoms of the water molecules.
26 citations
IBM1
TL;DR: In this article, the atom pair potentials were obtained from ab initio SCF-LCAO-MO calculations for model complexes of Mg2+ and Ca2+ with N, N-dimethylacetamide, and malonamide.
Abstract: Atom pair potentials are obtained from ab initio SCF-LCAO-MO calculations for model complexes of Mg2+ and Ca2+ with N, N-dimethylacetamide, and malonamide. The SCF-LCAO-MO interaction energies for 271 complexes of Mg2+ and 271 complexes of Ca2+ with these amides were fitted with a simple analytical potential by a least-square procedure. Interaction energies and optimal ion locations obtained by pair-potential calculations are compared with values obtained by ab initio calculations for some related amides. The application of the atom pair potentials to the structure of the Mg2+-complex [MgCl2 (C3H7ON)6] of N-ethylacetamide is discussed.
15 citations
IBM1
TL;DR: Despite the availability of fast computers for the last ten years, computations of Hartree-Fock quality wavefunctions (wf) for systems with more than 30 to 40 atoms are nonexistent as discussed by the authors.
Abstract: Despite the availability of fast computers for the last ten years, computations of Hartree-Fock quality wavefunctions (wf) for systems with more than 30 to 40 atoms are nonexistent, and very few examples of computations with 50 or more atoms are available at the minimal basis set level.
1 citations