Optimization of analytic density functionals by parallel genetic algorithm

We report the construction and implementation of a parallel genetic algorithm (PGA) for use in optimization of analytic density-functional theory. Our new algorithm demonstrates comparable performance to our previous simplex optimizer when benchmarked against the extended G2 set, and the considerable scatter between different optimizations shows that robust methods are required. This new PGA will allow us to further expand our parameter space while efficiently utilizing cluster and supercomputing resources as the problems grow larger.     

Self-consistent, constrained linear-combination-of-atomic-potentials approach to quantum mechanics

Variational fitting gives a stationary linear-combination of atomic potentials (LCAP) approximation to the Kohn-Sham (KS) potential, V. That potential is central to density-functional theory because it generates all orbitals, occupied as well as virtual. Perturbation theory links two self-consistent field (SCF) calculations that differ by the perturbation. Using the same variational LCAP methods and basis sets in the two SCF calculations gives precise KS potentials for each order. Variational V perturbation theory, developed herein through second order, gives stationary potentials at each order and stationary even-order perturbed energies that precisely link the two SCF calculations. Iterative methods are unnecessary because the dimension of the matrix that must be inverted is the KS basis size, not the number of occupied times virtual orbitals of coupled-perturbed methods. With variational perturbation theory, the precision of derivatives and the fidelity of the LCAP KS potential are not related. Finite differences of SCF calculations allow the precision of analytic derivatives from double-precision code to be verified to roughly seven significant digits. For a simple functional, the fourth derivatives of the energy and the first and second derivative of the KS potentials with respect to orbital occupation are computed for a standard set of molecules and basis sets, with and without constraints on the fit to the KS potential. There is no significant difference between the constrained and unconstrained calculations.     

Measurement of the spin-depairing interaction in Sn0.75Eu0.25Mo6S8

Mössbauer effect measurements of the ¹⁵¹ Eu resonance in the Chevrel phase superconductor Sn_0.75Eu_0.25Mo₆S₈ have been used to obtain the temperature dependence of the Eu paramagnetic relaxation rate. This consists of a temperature independent part arising from spin-spin interactions and a part linear in T due to the Korringa process. From the slope we obtain $\text{I}$ = 0.0033/Eu atom-spin, where $\text{I}$ is the exchange coupling between the rare-earth spin and the conduction electron spin, and N(E_F) is the local density of states. This value is roughly one order of magnetude lower than that measured in binary superconductors, and accounts for the very weak dependence of the transition temperature on magnetic impurity concentration.     

Hyperfine fields at sp sites in Clb Heusler alloys

Hyperfine fields have been measured at Cd, Sn and Sb sites in several Ni, Rh, Ir and Pt-based Heusler alloys. The Cd fields at 77 K were found to be ?95 k0e, ?108(4) k04, ±166(5) k0e and +196(9) k0e in RhMnSb, IrMnSn, IrMnSb and PtMnGa, respectively. Sn-site fields were found to be ±53(5) k0e and ±62(5) k0e in NiMnSb and PtMnSb, respectively, and the Sb-site fields, +276(5) k0e, +65(5) k0e and +210(5) k0e in NiMnSb, IrMnSb and PtMnSb, respectively. Results are discussed in terms of 5sp site hyperfine field systematics in Cl_b Heusler alloys.     

1,2,4-Triazoles—XXXIV: Photodimerization of some 1,2,4-triazo[4,3--]quinoline and 1,2,4-triazolo[3,4-a]isoquinoline derivatives

Irradiation of 1,2,4-triazolo[4,3-a]quinoline and several Me derivatives at 300 nm afforded the cisoid-fused, head-to-tail cyclobutane dimers 7bα,7cα,14bα,14cα - tetrahydro - 1,2,3a,8,9,10a - hexaazadibenzo [c,i]dicyclopenta[a,g]biphenylenes. However, 1,2,4 - triazolo[3,4-a]isoquinolines gave analogous cisoid-fused, head-to-head dimers except for the 5-Me derivative where the head-to-tail dimer was obtained.Codimerization occurred when 1 - methyl - 1,2,4 - triazolo[4,3-a]quinoline and 5 - methyl - 1,2,4 -triazolo[3,4-a]isoquinoline were irradiated at 300 nm, affording a cisoid-fused head-to-tail cyclobutane co-dimer as the single photoproduct. However, irradiation of their 5-Me substituted derivatives at 300 nm afforded the cisoid-fused, head-to-head, cyclobutane codimer and also a minor amount of the dimer derived from 5 - methyl -1,2,4- triazolo[4,3-a] quinoline. Irradiation of equimolar quantities of 2(1H)-quinolinone and 5 - methyl - 1,2,4 -triazolo [4,3-a]quinoline at 300 nm gave the known 2(1H)-quinolinone dimer and a minor amount of a cisoid-fused co-dimer of undetermined configuration.     

A sample-drying technique for room-temperature phosphorescence

The sample-drying procedure described improves the precision, decreases the time needed and reduces the expense of the solid-surface room-temperature phosphorescence technique. Samples are dried in a glovebg apparatus interfaced to the sample compartment of the spectrophotophosphorimeter. The samples are treated with sodium citrate to prevent moisture quenching the phosphorescence emission The relative standard deviations of measurements are reduced to less than 2% for large sets of samples. The total time required for 37 samples is only 5.5 h compared to 20 h by a conventional technique.