Structures of small water clusters using gradient-corrected density functional theory (original) (raw)
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Small Clusters of Water Molecules Using Density Functional Theory
The Journal of Physical Chemistry, 1996
The geometries, interaction energies, and harmonic vibrational frequencies of water clusters (with up to 8 molecules) have been studied using density functional theory (DFT) at the gradient corrected level. The water monomer and water dimer calculations have been used as benchmarks to investigate different choices for basis sets and density functionals. Our results for larger clusters agree with both available high-level ab initio calculations and experimental information. The calculations of the vibrational frequencies and IR absorption intensities for the larger clusters, for which no other reliable quantum-chemical calculation is available, are presented to facilitate the frequency assignment of experimental spectra.
Journal of Chemical Physics, 2008
Second order Møller-Plesset perturbation theory at the complete basis set limit and diffusion quantum Monte Carlo are used to examine several low energy isomers of the water hexamer. Both approaches predict the so-called prism to be the lowest energy isomer, followed by cage, book, and cyclic isomers. The energies of the four isomers are very similar, all being within 10-15 meV/ H 2 O. These reference data are then used to evaluate the performance of several density-functional theory exchange-correlation ͑xc͒ functionals. A subset of the xc functionals tested for smaller water clusters ͓I. Santra et al., J. Chem. Phys. 127, 184104 ͑2007͔͒ has been considered. While certain functionals do a reasonable job at predicting the absolute dissociation energies of the various isomers ͑coming within 10-20 meV/ H 2 O͒, none predict the correct energetic ordering of the four isomers nor does any predict the correct low total energy isomer. All xc functionals tested either predict the book or cyclic isomers to have the largest dissociation energies. A many-body decomposition of the total interaction energies within the hexamers leads to the conclusion that the failure lies in the poor description of van der Waals ͑dispersion͒ forces in the xc functionals considered. It is shown that the addition of an empirical pairwise ͑attractive͒ C 6 R −6 correction to certain functionals allows for an improved energetic ordering of the hexamers. The relevance of these results to density-functional simulations of liquid water is also briefly discussed.
Molecular-dynamics simulations of water clusters
Physica E: Low-dimensional Systems and Nanostructures, 2000
The local minimum geometries and corresponding energy values of water clusters, [(H2O)n, n = 2-8]; have been investigated by using the molecular dynamics simulation method. In the simulations two di erent potential energy functions of central-force model, CF and CF2, have been used. Particular attention was paid to investigate the e ectiveness of these two empirical potential energy functions. CF has been used for n = 2 only, whereas CF2 has been used for n = 2-8. The cage structure of the water clusters appear for n¿6.
Structure and vibrational spectra of small water clusters from first principles simulations
The Journal of Chemical Physics, 2010
The structure and vibrational spectra of ͑H 2 O͒ n ͑n =2-5͒ clusters have been studied based on first-principles molecular dynamics simulations. Trends of the cluster structures with the cluster size show that water molecules in cluster are bound more tightly. The vibrational spectra as a function of cluster size and temperature are obtained using Fourier transformation of the velocity autocorrelation function. Results of the clusters in ground state show that when the cluster size increases, the librational peaks shift to blue and the bonded intramolecular OH stretching bands shift to red due to the clusterization and hydrogen-bond strengthening. Meanwhile, there are no significant shifts in the intramolecular bending and free OH stretching modes, indicating that the free hydrogen atoms are insensitive to the local bonding environment. The temperature-dependent vibrational spectra, which exhibit similar behaviors from the dimer to pentamer, show that there are significant broadenings of the spectra with temperature caused by thermal motions. Moreover, different bands shift to different directions, where librational bands shift to red while bonded OH stretching bands shift to blue, although the blueshifts are quite small for the dimer and trimer.
Structural Mathematical Models of Water Clusters Regarding the Energy of Hydrogen Bonding
Nanotechnology research and practice, 2015
In this review it is reported about the research on the structure of intermolecular water cyclic associates (clusters) with general formula (Н2О)n and their charged ionic clusters [(Н2О)n] + and [(Н2О)n]-by means of computer modeling and spectroscopy methods as 1 Н-NMR, IR-spectroscopy, DNES, EXAFS-spectroscopy, X-Ray and neurons diffraction. The computer calculation of polyhedral nanoclusters (Н2О)n, where n = 3-20 are carried out. Based on this data the main structural mathematical models describing water structure (quasicrystalline, continious, fractal, fractal-clathrate) have been examined and some important physical characteristics were obtained. The average energy of hydrogen bonding (EH…O) between Н2О molecules in the process of cluster formation was measured by the DNES method compiles-0,1067±0,0011 eV. It was also shown that water clusters formed from 2 H2О were more stable, than those ones from Н2О due to isotopic effects of deuterium.
Structural Models of Water and Structuring of Nano-clusters Regarding the Energies of Hydrogen Bonds
Journal of Medicine, Physiology and Biophysics, 2015
In this review it is reported about the research on the structure of intermolecular water cyclic associates (clusters) with general formula (Н 2 О) n and their charged ionic clusters [H + (Н 2 О) n ] + and [OH-(Н 2 О) n ]by means of computer modeling and spectroscopy methods as 1 Н-NMR, IR-spectroscopy, NES, DNES, EXAFSspectroscopy, X-Ray and neurons diffraction. The computer calculation of polyhedral nanoclusters (Н 2 О) n , where n = 3-20 are carried out. Based on this data the main structural mathematical models describing water structure (quasi-crystalline, continuous, fractal, fractal-clathrate) have been examined and some important physical characteristics were obtained. The average energy of hydrogen bonding between Н 2 О molecules in the process of cluster formation was measured by the DNES method compiles-0.1067 ± 0.0011 eV. It was also shown that water clusters formed from D 2 О were more stable, than those ones from Н 2 О due to isotopic effects of deuterium.
Structure and some properties of small water clusters
Journal of Structural Chemistry, 1994
The energies and structures of many small water clusters (H20)n (n = 8-26) are calculated using the atom-atom potential functions suggested earlier. For each n, several stable configurations were found that differ in the number of H-bonds and in the topology of the graphs formed by such bonds. The clusters in which the molecules lie at the vertices of convex polyhedra have the lowest-energy but other configurations may have close or even lower energies. For the most stable clusters, the energy dependence on n is close to linear. At 300 K, the mean energies of the clusters behave similarly. Monte-Carlo simulations showed that the clusters undergo pseudomelting at approximately 200 K.
A Density Functional Theory for Studying Ionization Processes in Water Clusters
The Journal of Physical Chemistry A, 2011
A generalized Kohn-Sham (GKS) approach to density functional theory (DFT), based on the Baer-Neuhauser-Livshits range-separated hybrid, combined with ab initio motivated range-parameter tuning is used to study properties of water dimer and pentamer cations. The water dimer is first used as a benchmark system to check the approach. The present brand of DFT localizes the positive charge (hole), stabilizing the proton transferred geometry in agreement with recent coupled-cluster calculations. Relative energies of various conformers of the water dimer cation compare well with previously published coupled cluster results. The GKS orbital energies are good approximations to the experimental ionization potentials of the system. Low-lying excitation energies calculated from time-dependent DFT based on the present method compare well with recently published high-level "equation of motion-coupled-cluster" calculations. The harmonic frequencies of the water dimer cation are in good agreement with experimental and wave function calculations where available. The method is applied to study the water pentamer cation. Three conformers are identified: two are Eigen type and one is a Zundel type. The structure and harmonic vibrational structure are analyzed. The ionization dynamics of a pentamer water cluster at 0 K shows a fast <50 fs transient for transferring a proton from one of the water molecules, releasing a hydroxyl radical and creating a protonated tetramer carrying the excess hole.