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 critically review dissipative particle dynamics (DPD) as a mesoscopic simulation method. We have established useful parameter ranges for simulations, and have made a link between these parameters and χ-parameters in Flory-Huggins-type models. This is possible because the equation of state of the DPD fluid is essentially quadratic in density. This link opens the way to do large scale simulations, effectively describing millions of atoms, by firstly performing simulations of molecular fragments retaining all atomistic details to derive χ-parameters, then secondly using these results as input to a DPD simulation to study the formation of micelles, networks, mesophases and so forth. As an example application, we have calculated the interfacial tension σ between homopolymer melts as a function of χ and N and have found a universal scaling collapse when σ/ρkBTχ0.4 is plotted against χN for N>1. We also discuss the use of DPD to simulate the dynamics of mesoscopic systems, and indicate a possible problem with...

https://www.physics.iitm.ac.in/~iol/lecture_notes/groot-warren.pdf

Dissipative particle dynamics : bridging the gap between atomistic and mesoscopic simulation

We present an extensive molecular‐dynamics simulation for a bead spring model of a melt of linear polymers. The number of monomers N covers the range from N=5 to N=400. Since the entanglement length Ne is found to be approximately 35, our chains cover the crossover from the nonentangled to the entangled regime. The Rouse model provides an excellent description for short chains N<Ne, while the dynamics of the long chains can be described by the reptation model. By mapping the model chains onto chemical species we give estimates of the times and distances of onset of the slowing down in motion due to reptation. Comparison to neutron spin‐echo data confirm our mapping procedure, resolving a discrepancy between various experiments. By considering the primitive chain we are able to directly visualize the confinement to a tube. Analyzing the Rouse mode relaxation allows us to exclude the generalized Rouse models, while the original reptation prediction gives a good description of the data.

Dynamics of entangled linear polymer melts: A molecular‐dynamics simulation

https://www.tcd.ie/Physics/people/Graham.Cross/SF%20Poster%202011/Schuh-ActaMater07-Mechanical%20behaviour%20of%20amorphous%20alloys.pdf

Mechanical behavior of amorphous alloys

Block copolymers are all around us, found in such products as upholstery foam, adhesive tape and asphalt additives. This class of macromolecules is produced by joining two or more chemically distinct polymer blocks, each a linear series of identical monomers, that may be thermodynamically incompatible (like oil and vinegar). Segregation of these blocks on the molecular scale (5–100 nm) can produce astonishingly complex nanostructures, such as the “knitting pattern” shown on the cover of this issue of PHYSICS TODAY. This striking pattern, discovered by Reimund Stadler and his coworkers, reflects a delicate free‐energy minimization that is common to all block copolymer materials.

Block Copolymers—Designer Soft Materials

Simulations are reported for a system of n‐octanelike molecules at fixed volume, with various strengths of attractive potential. Spontaneous cavitation is observed to occur with the production of both cylindrical and lamellar cavities. The molecules are shown in all cases preferentially to align perpendicular to the cavity/liquid interface. The cavitated samples have a higher percentage of trans bonds in comparison with the homogeneous fluid samples.

Spontaneous cavitation in a n‐octanelike fluid

Considerations of the thermodynamics pertaining to the critical field of small superconducting samples of various shapes results in an explicit relation for the ratio of the critical field of small samples to that of bulk in terms of the magnetic moment. The magnetic moment has been calculated using Miller's modification of the Bardeen-Cooper-Schrieffer kernel which includes mean free path. The critical-field ratios of various shapes in decreasing order are sphere, cylinder in parallel field, cylinder in transverse field, and plate in parallel field. The findings are compatible with the fact that dislocations (cylinder like) may be the filaments responsible for hard superconductivity. Under certain conditions the filaments could be numerous and large enough for an appreciable fraction of the sample to appear superconducting in a specific heat measurement. The size of the filaments would also account for the lack of latent heat observed in hard superconductors. Because of the relative orientation of dislocations with respect to the applied field, not all dislocations will serve equally as filaments, thus explaining the current density vs critical-field curve and accounting for an anisotropic critical field when there is a preferred orientation of dislocations.

Eugene Helfand

Papers

Spontaneous cavitation in a n‐octanelike fluid

Critical Field of Thin Superconducting Shapes

Dilute polymer solution in steady shear flow: Non-Newtonian stress.

Critical Correlations in the Ising Model

Study of the pair correlation function diagrams