Enabling Large-Scale Condensed-Phase Hybrid Density Functional Theory Based Molecular Dynamics. 1. Theory, Algorithm, and Performance.

By including a fraction of exact exchange (EXX), hybrid functionals reduce the self-interaction error in semilocal density functional theory (DFT) and thereby furnish a more accurate and reliable description of the underlying electronic structure in systems throughout biology, chemistry, physics, and materials science. However, the high computational cost associated with the evaluation of all required EXX quantities has limited the applicability of hybrid DFT in the treatment of large molecules and complex condensed-phase materials. To overcome this limitation, we describe a linear-scaling approach that utilizes a local representation of the occupied orbitals (e.

Reactivity and Transformation of Antimetastatic and Cytotoxic Rhodium(III)-Dimethyl Sulfoxide Complexes in Biological Fluids: An XAS Speciation Study.

Rhodium(III) anticancer drugs can exert preferential antimetastatic or cytotoxic activities, which are dependent on subtle structural changes. In order to delineate factors affecting the biotransformations and speciation, mer,cis-[RhCl( S-dmso)( O-dmso)] (A1) and mer,cis-[RhCl( S-dmso)(N-indazole)] (A2) have been studied by X-ray absorption spectroscopy (XAS). Interactions of these complexes with saline buffer, cell culture media, serum proteins (albumin and apo-transferrin), native and chemically degraded collagen gels, and A549 cells have been studied using linear combination fitting (LCF) and 3D scatter plots of XAS data.

On the geometric dependence of the molecular dipole polarizability in water: A benchmark study of higher-order electron correlation, basis set incompleteness error, core electron effects, and zero-point vibrational contributions.

In this work, we investigate how geometric changes influence the static dipole polarizability () of a water molecule by explicitly computing the corresponding dipole polarizability surface (DPS) across 3125 total (1625 symmetry-unique) geometries using linear response coupled cluster theory including single, double, and triple excitations (LR-CCSDT) and the doubly augmented triple- basis set (d-aug-cc-pVTZ). Analytical formulae based on power series expansions of this surface are generated using linear least-squares analysis and provide highly accurate estimates of this quantity as a function of molecular geometry (i.e.

Unraveling substituent effects on the glass transition temperatures of biorenewable polyesters.

Converting biomass-based feedstocks into polymers not only reduces our reliance on fossil fuels, but also furnishes multiple opportunities to design biorenewable polymers with targeted properties and functionalities. Here we report a series of high glass transition temperature (T up to 184 °C) polyesters derived from sugar-based furan derivatives as well as a joint experimental and theoretical study of substituent effects on their thermal properties. Surprisingly, we find that polymers with moderate steric hindrance exhibit the highest T values.

Exploiting Molecular Weight Distribution Shape to Tune Domain Spacing in Block Copolymer Thin Films.

We report a method for tuning the domain spacing ( D) of self-assembled block copolymer thin films of poly(styrene- block-methyl methacrylate) (PS- b-PMMA) over a large range of lamellar periods. By modifying the molecular weight distribution (MWD) shape (including both the breadth and skew) of the PS block via temporal control of polymer chain initiation in anionic polymerization, we observe increases of up to 41% in D for polymers with the same overall molecular weight ( M ≈ 125 kg mol) without significantly changing the overall morphology or chemical composition of the final material. In conjunction with our experimental efforts, we have utilized concepts from population statistics and least-squares analysis to develop a model for predicting D based on the first three moments of the MWDs.

Different Ways of Hydrogen Bonding in Water - Why Does Warm Water Freeze Faster than Cold Water?

The properties of liquid water are intimately related to the H-bond network among the individual water molecules. Utilizing vibrational spectroscopy and modeling water with DFT-optimized water clusters (6-mers and 50-mers), 16 out of a possible 36 different types of H-bonds are identified and ordered according to their intrinsic strength. The strongest H-bonds are obtained as a result of a concerted push-pull effect of four peripheral water molecules, which polarize the electron density in a way that supports charge transfer and partial covalent character of the targeted H-bond.

Vibrational Spectra of Molecular Crystals with the Generalized Energy-Based Fragmentation Approach.

The generalized energy-based fragmentation (GEBF) approach for molecular crystals with periodic boundary condition (PBC) (denoted as PBC-GEBF) is extended to allow vibrational spectra of molecular crystals to be easily computed at various theory levels. Within the PBC-GEBF approach, the vibrational frequencies of a molecular crystal can be directly evaluated from molecular quantum chemistry calculations on a series of nonperiodic molecular systems. With this approach, the vibrational spectra of molecular crystals can be calculated with much reduced computational costs at various theory levels, as compared to those required by the methods based on periodic electronic structure theory.