arXiv subjects

Rasmus A. X. Persson

Publications and source records attributed to Rasmus A. X. Persson.

8 recordsLinked to original sources

arXiv2024

Commment on "Secondary Nucleation by Interparticle Energies. I. Thermodynamics"

We point out an inconsistency in the theoretical treatment of Bosetti and collaborators (Crystal Growth & Design, 2021, 22.1: 87-97), and then proceed to prove that for monomers interacting by two-body potentials, the presence of an infinite, flat, attractive crystal surface may not induce an increased propensity for cluster formation (that is, secondary nucleation) of the type envisioned by these authors.

cond-mat.stat-mech↗

arXiv2022

Note on the physical basis of spatially resolved thermodynamic functions

The spatial resolution of extensive thermodynamic functions is discussed. A physical definition of the spatial resolution based on a spatial analogy of partial molar quantities is advocated, which is shown to be consistent with how hydration energies are typically spatially resolved in the molecular simulation literature. It is then shown that, provided the solvent is not at a phase transition, the spatially resolved entropy function calculated by first-order grid inhomogeneous solvation theory (Nguyen et al. J. Chem. Phys., 137, 044101 [2012]) satisfies the definition rigorously, whereas that calculated by grid cell theory (Gerogiokas et al., J. Chem. Theory Comput., 10, 35 [2014]) most likely does not. Moreover, for an ideal gas in an external field, the former theory is shown consistent in the limit of weak field or high temperature whereas the latter is not. Finally, consistent with the proposed definition and with the case of an ideal gas in an external field, we derive an approximate expression for the solvent contribution to the free energy of solvation in the limit of infinite dilution from the spatial variation of the density around the solute.

cond-mat.stat-mech↗

arXiv2017

Bibliometric author evaluation through linear regression on the coauthor network

The rising trend of coauthored academic works obscures the credit assignment that is the basis for decisions of funding and career advancements. In this paper, a simple model based on the assumption of an unvarying "author ability" is introduced. With this assumption, the weight of author contributions to a body of coauthored work can be statistically estimated. The method is tested on a set of some more than five-hundred authors in a coauthor network from the CiteSeerX database. The ranking obtained agrees fairly well with that given by total fractional citation counts for an author, but noticeable differences exist.

cs.DL↗

arXiv2013

Comment on "Calculation of microcanonical entropy differences from configurational averages"

We introduce a simple improvement on the method to calculate equilibrium entropy differences between classical energy levels proposed by Davis (S. Davis, Phys. Rev. E, 050101, 2011). We demonstrate that the modification is superior to the original whenever the energy levels are sufficiently closely spaced or whenever the microcanonical averaging needed in the method is carried out by importance sampling Monte Carlo. We also point out the necessary adjustments if Davis's method (improved or not) is to be used with molecular dynamics simulations.

physics.comp-ph↗

arXiv2012

Perturbation method to calculate the density of states

Monte Carlo switching moves ("perturbations") are defined between two or more classical Hamiltonians sharing a common ground-state energy. The ratio of the density of states (DOS) of one system to that of another is related to the ensemble averages of the microcanonical acceptance probabilities of switching between these Hamiltonians, analogously to the case of Bennett's acceptance ratio method for the canonical ensemble [C. H. Bennett, J. Comput. Phys., 22, 245 (1976)]. Thus, if the DOS of one of the systems is known, one obtains those of the others and, hence, the partition functions. As a simple test case, the vapor pressure of an anharmonic Einstein crystal is computed, using the harmonic Einstein crystal as the reference system in one dimension; an auxiliary calculation is also performed in three dimensions. As a further example of the algorithm, the energy dependence of the ratio of the DOS of the square-well and hard-sphere tetradecamers is determined, from which the temperature dependence of the constant-volume heat capacity of the square-well system is calculated and compared with canonical Metropolis Monte Carlo estimates. For these cases and reference systems, the perturbation calculations exhibit a higher degree of convergence per Monte Carlo cycle than Wang-Landau (WL) sampling, although for the one-dimensional oscillator the WL sampling is ultimately more efficient for long runs. Last, we calculate the vapor pressure of liquid gold using an empirical Sutton-Chen many-body potential and the ideal gas as the reference state. Although this proves the general applicability of the method, by its inherent perturbation approach, the algorithm is suitable for those particular cases where the properties of a related system are well known.

physics.comp-ph↗

arXiv2012

Modification of the Gay-Berne potential for improved accuracy and speed

A modification of the Gay-Berne potential is proposed which is about 10% to 20% more speed efficient (that is, the original potential runs 15% to 25% slower, depending on architecture) and statistically more accurate in reproducing the energy of interaction of two linear Lennard-Jones tetratomics when averaged over all orientations. For the special cases of end-to-end and side-by-side configurations, the new potential is equivalent to the Gay-Berne one.

physics.chem-ph↗

arXiv2011

On the Physical Cluster of Nucleation Theory: Generalized Hill Cluster

The physical cluster originally conceived by Hill (J. Chem. Phys, 23, 617) is generalized for the case $N > 2$ in a novel way. Contrary to Hill's pairwise generalization, this definition assures that all constituent molecules of the cluster have insufficient kinetic energy to escape, and avoids the spurious implication of Hill's generalization that the molecular velocities are to be increasingly equal.

cond-mat.stat-mech↗

arXiv2010

Gaussian-Charge Polarizable Interaction Potential for Carbon Dioxide

A number of simple pair interaction potentials of the carbon dioxide molecule are investigated and found to underestimate the magnitude of the second virial coefficient in the temperature interval 220 K to 448 K by up to 20%. Also the third virial coefficient is underestimated by these models. A rigid, polarizable, three-site interaction potential reproduces the experimental second and third virial coefficients to within a few percent. It is based on the modified Buckingham exp-6 potential, an anisotropic Axilrod-Teller correction and Gaussian charge densities on the atomic sites with an inducible dipole at the center of mass. The electric quadrupole moment, polarizability and bond distances are set to equal experiment. Density of the fluid at 200 and 800 bars pressure is reproduced to within some percent of observation over the temperature range 250 K to 310 K. The dimer structure is in passable agreement with electronically resolved quantum-mechanical calculations in the literature, as are those of the monohydrated monomer and dimer complexes using the polarizable GCPM water potential. Qualitative agreement with experiment is also obtained, when quantum corrections are included, for the relative stability of the trimer conformations, which is not the case for the pair potentials.

cond-mat.mtrl-sci↗