6.2.2. Definition of Effective Properties 3064 6.3. Response Properties to Magnetic Fields 3066 6.3.1. Nuclear Shielding 3066 6.3.2. Indirect Spin−Spin Coupling 3067 6.3.3. EPR Parameters 3068 6.4. Properties of Chiral Systems 3069 6.4.1. Electronic Circular Dichroism (ECD) 3069 6.4.2. Optical Rotation (OR) 3069 6.4.3. VCD and VROA 3070 7. Continuum and Discrete Models 3071 7.1. Continuum Methods within MD and MC Simulations 3072

/pdf/quantum-mechanical-continuum-solvation-models-3edv963g14.pdf

Quantum mechanical continuum solvation models.

We present a new continuum solvation model based on the quantum mechanical charge density of a solute molecule interacting with a continuum description of the solvent. The model is called SMD, where the “D” stands for “density” to denote that the full solute electron density is used without defining partial atomic charges. “Continuum” denotes that the solvent is not represented explicitly but rather as a dielectric medium with surface tension at the solute−solvent boundary. SMD is a universal solvation model, where “universal” denotes its applicability to any charged or uncharged solute in any solvent or liquid medium for which a few key descriptors are known (in particular, dielectric constant, refractive index, bulk surface tension, and acidity and basicity parameters). The model separates the observable solvation free energy into two main components. The first component is the bulk electrostatic contribution arising from a self-consistent reaction field treatment that involves the solution of the nonho...

Universal solvation model based on solute electron density and on a continuum model of the solvent defined by the bulk dielectric constant and atomic surface tensions.

CHARMM (Chemistry at HARvard Molecular Mechanics) is a highly versatile and widely used molecu- lar simulation program. It has been developed over the last three decades with a primary focus on molecules of bio- logical interest, including proteins, peptides, lipids, nucleic acids, carbohydrates, and small molecule ligands, as they occur in solution, crystals, and membrane environments. For the study of such systems, the program provides a large suite of computational tools that include numerous conformational and path sampling methods, free energy estima- tors, molecular minimization, dynamics, and analysis techniques, and model-building capabilities. The CHARMM program is applicable to problems involving a much broader class of many-particle systems. Calculations with CHARMM can be performed using a number of different energy functions and models, from mixed quantum mechanical-molecular mechanical force fields, to all-atom classical potential energy functions with explicit solvent and various boundary conditions, to implicit solvent and membrane models. The program has been ported to numer- ous platforms in both serial and parallel architectures. This article provides an overview of the program as it exists today with an emphasis on developments since the publication of the original CHARMM article in 1983.

/pdf/charmm-the-biomolecular-simulation-program-4kexem0xkx.pdf

CHARMM: the biomolecular simulation program.

Advancing perovskite solar cell technologies toward their theoretical power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, we suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extraction at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on average, with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of our perovskite solar cells was conducted in air and from solution at low temperatures, which should simplify manufacturing of large-area perovskite devices that are inexpensive and perform at high levels.

http://science.sciencemag.org/content/sci/345/6196/542.full.pdf

Interface engineering of highly efficient perovskite solar cells

We present an improved and extended version of our coarse grained lipid model. The new version, coined the MARTINI force field, is parametrized in a systematic way, based on the reproduction of partitioning free energies between polar and apolar phases of a large number of chemical compounds. To reproduce the free energies of these chemical building blocks, the number of possible interaction levels of the coarse-grained sites has increased compared to those of the previous model. Application of the new model to lipid bilayers shows an improved behavior in terms of the stress profile across the bilayer and the tendency to form pores. An extension of the force field now also allows the simulation of planar (ring) compounds, including sterols. Application to a bilayer/cholesterol system at various concentrations shows the typical cholesterol condensation effect similar to that observed in all atom representations.

/pdf/the-martini-force-field-coarse-grained-model-for-3l11ncr3fg.pdf

The MARTINI force field : Coarse grained model for biomolecular simulations

The SM5.4, SM5.2R, and SM5.0R solvation models are applied to calculate the vapor pressure of 156 molecules. This provides a test of the solvation models, buteven more soit provides a useful scheme for estimating the vapor pressure at 298 K of any organic molecule for which a few standard descriptors are known or can be estimated.

Prediction of Vapor Pressures from Self-Solvation Free Energies Calculated by the SM5 Series of Universal Solvation Models

We present a new class IV charge model. The model, called Charge Model 3 (CM3), is designed to be able to obtain accurate partial charges from hybrid density functional calculations with a variable amount of Hartree−Fock exchange and with or without diffuse functions in the basis. The model maps atomic partial charges obtained by Lowdin or redistributed Lowdin population analysis into improved (class IV) charges that reproduce accurate charge-dependent observables for molecules containing H, Li, C, N, O, F, Si, S, P, Cl, and Br. The hybrid density functional theory we use here is based on Adamo and Barone's modified Perdew−Wang (mPW) gradient-corrected exchange functional and the PW91 gradient corrected correlation functional. These parametrizations can be used with any arbitrary fraction of Hartree−Fock exchange in conjunction with any of the five basis sets, MIDI!, MIDI!6D, 6-31G*, 6-31+G*, and 6-31+G**. We also present two parametrizations for Hartree−Fock theory employing the MIDI!6D and 6-31G* basis ...

Charge Model 3: A class IV Charge Model based on hybrid density functional theory with variable exchange

Our extension of the AM1 semiempirical molecular orbital technique, AM1*, has been parameterized for the elements Al, Si, Ti and Zr. The basis sets for all four metals contain a set of d-orbitals. Thus, AM1* parameters are now available for H, C, N, O and F (which use the original AM1 parameters), Al, Si, P, S, Cl, Ti, Mo and Zr. Special attention was paid to reproducing homolytic and heterolytic bond-dissociation energies correctly. Such bond-energy data help to avoid eccentricities in the parameterization caused by inaccurate experimental heats of formation. The performance and typical errors of AM1* for the newly parameterized elements are discussed. Generally, the new method performs less well than established techniques for heats of formation but considerably better for the heats of reaction.

AM1* parameters for aluminum, silicon, titanium and zirconium.

The development and application of phosphorescent emitters in organic light-emitting diodes (OLEDs) have played a critical role in the push to commercialization of OLED-based display and lighting technologies. Here, we use density functional theory methods to study how modifying the ancillary ligand influences the electronic and photophysical properties of heteroleptic bis(4,6-difluorophenyl) pyridinato-N,C [dfppy] iridium(III) complexes. We examine three families of bidentate ancillary ligands based on acetylacetonate, picolinate, and pyridylpyrazolate. It is found that the frontier molecular orbitals of the heteroleptic complexes can be substantially modulated both as a function of the bidentate ligand family and of the substitution patterns within a family. As a consequence, considerable control over the first absorption and phosphorescence emission transitions, both of which are dominated by one-electron transitions between the HOMO and LUMO, is obtained. Tuning the nature of the ancillary ligand, therefore, can be used to readily modulate the photophysical properties of the emitters, providing a powerful tool in the design of the emitter architecture.

Tuning the electronic and photophysical properties of heteroleptic iridium(III) phosphorescent emitters through ancillary ligand substitution: a theoretical perspective

Using a database of 440 molecules, we develop a set of effective solvent descriptors that characterize the organic carbon component of soil and thereby allow quantum mechanical SM5 universal solvation models to be applied to partitioning of solutes between soil and air. Combining this set of effective solvent descriptors with solute atomic surface tension parameters already developed for water/air and organic solvent/air partitioning allows one to predict the partitioning of any solutes composed of H, C, N, O, F, P, S, Cl, Br, and I between soil and water. We also present linear correlations of soil/water partitioning with 1-octanol/water partition coefficients using the same database. The quantum mechanical calculations have the advantages that they require no experimental input and should be robust for a wide range of solute functionality. The quantitative effective solvent descriptors can be used for a better understanding (than with previously available models) of the sources of different partitioning...

Paul Winget

Papers

Prediction of Vapor Pressures from Self-Solvation Free Energies Calculated by the SM5 Series of Universal Solvation Models

Charge Model 3: A class IV Charge Model based on hybrid density functional theory with variable exchange

AM1* parameters for aluminum, silicon, titanium and zirconium.

Tuning the electronic and photophysical properties of heteroleptic iridium(III) phosphorescent emitters through ancillary ligand substitution: a theoretical perspective

Prediction of soil sorption coefficients using a universal solvation model