Assessment of density functional approximations for the hemibonded structure of water dimer radical cation

Due to the severe self-interaction errors associated with some density functional approximations, conventional density functionals often fail to dissociate the hemibonded structure of water dimer radical cation (H2O)2+ into the correct fragments: H2O and H2O+. Consequently, the binding energy of the hemibonded structure (H2O)2+ is not well-defined. For a comprehensive comparison of different functionals for this system, we propose three criteria: (i) The binding energies, (ii) the relative energies between the conformers of the water dimer radical cation, and (iii) the dissociation curves predicted by different functionals. The long-range corrected (LC) double-hybrid functional, omegaB97X-2(LP) [J.-D. Chai and M. Head-Gordon, J. Chem. Phys., 2009, 131, 174105.], is shown to perform reasonably well based on these three criteria. Reasons that LC hybrid functionals generally work better than conventional density functionals for hemibonded systems are also explained in this work.Comment: 10 pages, 5 figures, 4 table

The Eight-Vertex Model and Lattice Supersymmetry

We show that the XYZ spin chain along the special line of couplings J x J y +J x J z +J y J z =0 possesses a hidden $\mathcal{N}=(2,2)$ supersymmetry. This lattice supersymmetry is non-local and changes the number of sites. It extends to the full transfer matrix of the corresponding eight-vertex model. In particular, it is shown how to derive the supercharges from Baxter's Bethe ansatz. This analysis leads to new conjectures concerning the ground state for chains of odd length. We also discuss a correspondence between the spectrum of this XYZ chain and that of a manifestly supersymmetric staggered fermion chai

Assessment of density functional methods with correct asymptotic behavior

Long-range corrected (LC) hybrid functionals and asymptotically corrected (AC) model potentials are two distinct density functional methods with correct asymptotic behavior. They are known to be accurate for properties that are sensitive to the asymptote of the exchange-correlation potential, such as the highest occupied molecular orbital energies and Rydberg excitation energies of molecules. To provide a comprehensive comparison, we investigate the performance of the two schemes and others on a very wide range of applications, including the asymptote problems, self-interaction-error problems, energy-gap problems, charge-transfer problems, and many others. The LC hybrid scheme is shown to consistently outperform the AC model potential scheme. In addition, to be consistent with the molecules collected in the IP131 database [Y.-S. Lin, C.-W. Tsai, G.-D. Li, and J.-D. Chai, J. Chem. Phys., 2012, 136, 154109], we expand the EA115 and FG115 databases to include, respectively, the vertical electron affinities and fundamental gaps of the additional 16 molecules, and develop a new database AE113 (113 atomization energies), consisting of accurate reference values for the atomization energies of the 113 molecules in IP131. These databases will be useful for assessing the accuracy of density functional methods.Comment: accepted for publication in Phys. Chem. Chem. Phys., 46 pages, 4 figures, supplementary material include

Thermally-assisted-occupation density functional theory with generalized-gradient approximations

We extend the recently proposed thermally-assisted-occupation density functional theory (TAO-DFT) [J.-D. Chai, J. Chem. Phys. 136, 154104 (2012)] to generalized-gradient approximation (GGA) exchange-correlation density functionals. Relative to our previous TAO-LDA (i.e., the local density approximation to TAO-DFT), the resulting TAO-GGAs are significantly superior for a wide range of applications, such as thermochemistry, kinetics, and reaction energies. For noncovalent interactions, TAO-GGAs with empirical dispersion corrections are shown to yield excellent performance. Due to their computational efficiency for systems with strong static correlation effects, TAO-LDA and TAO-GGAs are applied to study the electronic properties (e.g., the singlet-triplet energy gaps, vertical ionization potentials, vertical electron affinities, fundamental gaps, and symmetrized von Neumann entropy) of acenes with different number of linearly fused benzene rings (up to 100), which is very challenging for conventional electronic structure methods. The ground states of acenes are shown to be singlets for all the chain lengths studied here. With the increase of acene length, the singlet-triplet energy gaps, vertical ionization potentials, and fundamental gaps decrease monotonically, while the vertical electron affinities and symmetrized von Neumann entropy (i.e., a measure of polyradical character) increase monotonically.Comment: 27 pages, 15 figures, 3 tables, supplementary material not included. This is an extension of our previous work [e.g., see arXiv:1201.4866

Hybrid Feedback Control Methods for Robust and Global Power Conversion

In this paper, the applicability and importance of hybrid system tools for the design of control algorithms for energy conversion in power systems is illustrated in two hybrid control designs, one pertaining to DC/DC conversion and the other to DC/AC inversion. In particular, the mathematical models considered consist of constrained switched differential equations/inclusions that include all possible modes of operation of the systems. Furthermore, the obtained models can be analyzed and their algorithms designed using hybrid system tools so as to attain key desired properties, such as stability, forward invariance, global convergence, and robustness. We argue that hybrid system tools provide a systematic approach for analysis and controller design of power systems. In particular, hybrid system tools usually leads to power quantities that have better performance and robustness to state perturbations. Furthermore, they provide guidelines on how to tune the controller parameters based on design requirements. These factors motivate the implementation of the proposed hybrid controllers in modern power conversion systems that use renewable energy sources. Simulations illustrating the main results and benchmark tests are included

Genetic diversity of Jatropha curcas collections from different islands in Indonesia

Jatropha curcas L. is a potential bioenergy crop but has a lack of improved cultivars with high yields and oil content. Therefore, increasing our understanding of J. curcas germplasm is important for designing breeding strategies. This study was performed to investigate the genetic diversity and population structure of Indonesian J. curcas populations from six different islands. To construct a reference, we de novo assembled the scaffolds (N50 = 355.5 kb) using 182 Gb Illumina HiSeq sequencing data from Thai J. curcas variety Chai Nat. Genetic diversity analysis among 52 Indonesian J. curcas accessions was conducted based on yield traits and single nucleotide polymorphism (SNP) markers detected by mapping genotyping-by-sequencing reads from Indonesian population to Chai Nat scaffolds. Strong variation in yield traits was detected among accessions. Using J. integerrima as an outgroup, 13,916 SNPs were detected. Among J. curcas accessions, including accessions from other countries (Thailand, the Philippines and China), 856 SNPs were detected, but only 297 SNPs were detected among Indonesian J. curcas populations, representing low genetic diversity. Through phylogenetic and structural analysis, the populations were clustered into two major groups. Group one consists of populations from Bangka and Sulawesi in the northern part of Indonesia, which are located at a distance of 1572.59 km. Group two contains populations from islands in the southern part: Java, Lombok-Sumbawa, Flores and Timor. These results indicate that introduction of diverse J. curcas germplasms is necessary for the improvement of the genetic variation in the Indonesian collections

A Note on Pretzelosity TMD Parton Distribution

We show that the transverse-momentum-dependent parton distribution, called as Pretzelosity function, is zero at any order in perturbation theory of QCD for a single massless quark state. This implies that Pretzelosity function is not factorized with the collinear transversity parton distribution at twist-2, when the struck quark has a large transverse momentum. Pretzelosity function is in fact related to collinear parton distributions defined with twist-4 operators. In reality, Pretzelosity function of a hadron as a bound state of quarks and gluons is not zero. Through an explicit calculation of Pretzelosity function of a quark combined with a gluon nonzero result is found.Comment: improved explanation, published version in Phys. Lett.