The locality of the fourth root of staggered fermion determinant in the interacting case

The fourth root approximation in LQCD simulations with dynamical staggered fermions requires justification. We test its validity numerically in the interacting theory in a renormalization group framework.Comment: 6 pages, Talk presented at Lattice 2005 (Machines and Algorithms

Broken-Symmetry Unrestricted Hybrid Density Functional Calculations on Nickel Dimer and Nickel Hydride

In the present work we investigate the adequacy of broken-symmetry unrestricted density functional theory (DFT) for constructing the potential energy curve of nickel dimer and nickel hydride, as a model for larger bare and hydrogenated nickel cluster calculations. We use three hybrid functionals: the popular B3LYP, Becke's newest optimized functional Becke98, and the simple FSLYP functional (50% Hartree-Fock and 50% Slater exchange and LYP gradient-corrected correlation functional) with two basis sets: all-electron (AE) Wachters+f basis set and Stuttgart RSC effective core potential (ECP) and basis set. We find that, overall, the best agreement with experiment, comparable to that of the high-level CASPT2, is obtained with B3LYP/AE, closely followed by Becke98/AE and Becke98/ECP. FSLYP/AE and B3LYP/ECP give slightly worse agreement with experiment, and FSLYP/ECP is the only method among the ones we studied that gives an unaceptably large error, underestimating the dissociation energy of nickel dimer by 28%, and being in the largest disagreement with the experiment and the other theoretical predictions.Comment: 17 pages, 7 tables, 7 figures; submitted to J. Chem. Phys.; Revtex4/LaTeX2e. v2 (8/5/04): New (and better) ECP results, without charge density fitting (which was found to give large errors). Subtracted the relativistic corrections from all experimental value

The QCD equation of state with asqtad staggered fermions

We report on our result for the equation of state (EOS) with a Symanzik improved gauge action and the asqtad improved staggered fermion action at $N_t=4$ and 6. In our dynamical simulations with 2+1 flavors we use the inexact R algorithm and here we estimate the finite step-size systematic error on the EOS. Finally we discuss the non-zero chemical potential extension of the EOS and give some preliminary results.Comment: 7 pages, 6 figures, presented at Lattice2006(High Temperature and Density), to appear in Proceedings of Scienc