Correlation effects in quasi one dimensional electron wires

We explore the role of electron correlation in quasi one dimensional quantum wires as the range of the interaction potential is changed and their thickness is varied by performing exact quantum Monte Carlo simulations at various electronic densities. In the case of unscreened interactions with a long range 1/x tail there is a crossover from a liquid to a quasi Wigner crystal state as the density decreases. When this interaction is screened, quasi long range order is prevented from forming, although a significant correlation with 4 k_F periodicity is still present at low densities. At even lower electron concentration, exchange is suppressed and the spin-dependent interactions become negligible, making the electrons behave like spinless fermions. We show that this behavior is shared by the long range and screened interactions by studying the spin and charge excitations of the system in both cases. Finally, we study the effect of electron correlations in the double quantum wire experiment [Steinberg et al., Phys. Rev. B 77, 113307 (2006)], by introducing an accurate model for the screening in the experiment and explicitly including the finite length of the system in our simulations. We find that decreasing the electron density drives the system from a liquid to a state with quite strong 4 k_F correlations. This crossover takes place around $20 \mu m^{-1}$, the density where the electron localization occurs in the experiment. The charge and spin velocities are also in remarkable agreement with the experimental findings in the proximity of the crossover. We argue that correlation effects play an important role at the onset of the localization transition.Comment: minor improvements, 13 pages, 12 figure

Noncovalent Interactions by QMC: Speedup by One-Particle Basis-Set Size Reduction

While it is empirically accepted that the fixed-node diffusion Monte-Carlo (FN-DMC) depends only weakly on the size of the one-particle basis sets used to expand its guiding functions, limits of this observation are not settled yet. Our recent work indicates that under the FN error cancellation conditions, augmented triple zeta basis sets are sufficient to achieve a benchmark level of 0.1 kcal/mol in a number of small noncovalent complexes. Here we report on a possibility of truncation of the one-particle basis sets used in FN-DMC guiding functions that has no visible effect on the accuracy of the production FN-DMC energy differences. The proposed scheme leads to no significant increase in the local energy variance, indicating that the total CPU cost of large-scale benchmark noncovalent interaction energy FN-DMC calculations may be reduced.Comment: ACS book chapter, accepte

Manipulating the Tomonaga-Luttinger exponent by electric field modulation

We establish a theoretical framework for artificial control of the power-law singularities in Tomonaga-Luttinger liquid states. The exponent governing the power-law behaviors is found to increase significantly with an increase in the amplitude of the periodic electric field modulation applied externally to the system. This field-induced shift in the exponent indicates the tunability of the transport properties of quasi-one-dimensional electron systems.Comment: 7 pages, 3 figure

Envisioning a World Beyond APCs/BPCs

This archival page includes documents and recordings related to the international symposium, “Envisioning a World Beyond APCs/BPCs,” held in Lawrence, Kansas, on Thursday and Friday, November 17-18. The presenters were a group of 18 internationally respected scholars, publishers, university librarians, and executives from foundations and organizations, who were asked to participate in a discussion about current models available for achieving an expansive, inclusive, and balanced worldwide open publishing ecosystem. The symposium was co-sponsored by the University of Kansas Libraries, Open Access Network (a project of K|N Consultants), Allen Press, SPARC, and ARL. The materials included here are the symposium schedule, recordings of Parts 1 and 2 of the Nov. 17 livestream, a transcript of the livestream, and team proposals originating from the Nov. 18 morning session.This symposium was sponsored by the University of Kansas Libraries, Open Access Network (a project of K|N Consultants), Allen Press, and SPARC

Diffusion Monte Carlo Study of Para -Diiodobenzene Polymorphism Revisited

We revisit our investigation of the diffusion Monte Carlo (DMC) simulation of p-DIB molecular crystal polymorphism. [J. Phys. Chem. Lett. 2010, 1, 1789-1794] We perform, for the first time, a rigorous study of finite-size effects and choice of nodal surface on the prediction of polymorph stability in molecular crystals using fixed-node DMC. Our calculations are the largest which are currently feasible using the resources of the K computer and provide insights into the formidable challenge of predicting such properties from first principles. In particular, we show that finite-size effects can influence the trial nodal surface of a small (1×1×1) simulation cell considerably. We therefore repeated our DMC simulations with a 1×3×3 simulation cell, which is the largest such calculation to date. We used a DFT nodal surface generated with the PBE functional and we accumulated statistical samples with ∼6.4×105 core-hours for each polymorph. Our final results predict a polymorph stability consistent with experiment, but indicate that results in our previous paper were somewhat fortuitous. We analyze the finite-size errors using model periodic Coulomb (MPC) interactions and kinetic energy corrections, according to the CCMH scheme of Chiesa, Ceperley, Martin, and Holzmann. We investigate the dependence of the finite-size errors on different aspect ratios of the simulation cell (k-mesh convergence) in order to understand how to choose an appropriate ratio for the DMC calculations. Even in the most expensive simulations currently possible, we show that the finite size errors in the DMC total energies are far larger than the energy difference between the two polymorphs, although error cancellation means that the polymorph prediction is accurate. Finally, we found that the T-move scheme is essential for these massive DMC simulations in order to circumvent population explosions and large time-step biases.Chemistry and Chemical Biolog

The future of academic publishing: application of the long-tail theory

Print academic journals are dead. As we watch large metropolitan newspapers fail (as are many small town newspapers), the same economic forces are driving online scholarly publishing. This phenomenon is more than print journals going online. The options available with new low-cost online publishing software and the rise in the ability to use ratings from user generated content suggest more near-term changes are likely. Many of the outcomes are unsettled: the economics of online publishing; the standards for peer review, rank, and tenure; and the very nature of scholarly publishing itself. What is certain, however, is that the economics of online academic publishing—modeled via Anderson’s Long Tail Theory—will make it possible to provide greater access, more collaboration, and, ultimately, improved research and researchers. Universities acting as publishing centers with their e-reserves will be expected to change their faculty evaluations, providing greater academic rewards for those who act as editors, reviewers, and proofreaders within this new born-online and only-online world