Ab initio potential energy and dipole moment surfaces for CS2: determination of molecular vibrational energies.

The ground state potential energy and dipole moment surfaces for CS2 have been determined at the CASPT2/C:cc-pVTZ,S:aug-cc-pV(T+d)Z level of theory. The potential energy surface has been fit to a sum-of-products form using the neural network method with exponential neurons. A generic interface between neural network potential energy surface fitting and the Heidelberg MCTDH software package is demonstrated.

Atomistic models of ion and solute transport by the sodium-dependent secondary active transporters.

The recent determination of high-resolution crystal structures of several transporters offers unprecedented insights into the structural mechanisms behind secondary transport. These proteins utilize the facilitated diffusion of the ions down their electrochemical gradients to transport the substrate against its concentration gradient. The structural studies revealed striking similarities in the structural organization of ion and solute binding sites and a well-conserved inverted-repeat topology between proteins from several gene families.

The structural pathway for water permeation through sodium-glucose cotransporters.

Although water permeation across cell membranes occurs through several types of membrane proteins, the only permeation mechanism resolved at atomic scale is that through aquaporins. Crystallization of the Vibrio parahaemolyticus sodium-galactose transporter (vSGLT) allows investigation of putative water permeation pathways through both vSGLT and the homologous human Na-glucose cotransporter (hSGLT1) using computational methods. Grand canonical Monte Carlo and molecular dynamics simulations were used to stably insert water molecules in both proteins, showing the presence of a water-filled pathway composed of ∼100 water molecules.

Molecular dynamics simulations of DNA/PEI complexes: effect of PEI branching and protonation state.

Complexes formed by DNA and polyethylenimine (PEI) are of great research interest because of their application in gene therapy. In this work, we carried out all-atom molecular dynamics simulations to study eight types of DNA/PEI complexes, each of which was formed by one DNA duplex d(CGCGAATTCGCG)(2) and one PEI. We used eight different PEIs with four different degrees of branching and two protonation ratios of amine groups (23% and 46%) in the simulations to investigate how the branching degree and protonation state can affect the binding.

Weakly bound complexes trapped in quantum matrices: Structure, energetics, and isomer coexistence in (para-H(2))(N)(ortho-D(2))(3) clusters.

The ground state of mixed (para-H(2))(N)(ortho-D(2))(3) clusters of sizes ranging from N=8 to 37 is examined by means of the path integral ground state method. The chemical potential is calculated and reveals that magic numbers are consistent with those found in pure para-H(2) and ortho-D(2) clusters. The structural features of the mixed clusters are examined by analyzing density profiles, one-dimensional Pekeris distribution functions of the (ortho-D(2))(3) subsystem, and by direct visualization of density isosurfaces of the systems.

On the solid- and liquidlike nature of quantum clusters in their ground state.

The ground state of pristine clusters of (paraH(2))(N) and (orthoD(2))(N) of size ranging from N=11 to 55 is examined by means of the variational path integral method. The chemical potential is calculated for two different interaction models and it is shown that the location of magic numbers indeed depends on the chosen interaction potential. Density profiles are calculated and reveal the difference between the two isotopes with regards to shell structure.

Path integral ground state study of finite-size systems: application to small (parahydrogen)N (N=2-20) clusters.

We use the path integral ground state method to study the energetic and structural properties of small para-H2 clusters of sizes ranging from 2 to 20 molecules. A fourth order formula is used to approximate the short imaginary-time propagator and two interaction potentials are considered. Our results are compared to those of exact basis set calculations and other quantum Monte Carlo methods when available.

Path integral ground state with a fourth-order propagator: application to condensed helium.

Ground state properties of condensed helium are calculated using the path integral ground state (PIGS) method. A fourth-order approximation is used as short (imaginary) time propagator. We compare our results with those obtained with other quantum Monte Carlo (QMC) techniques and different propagators.