Some Observations on the Performance of the Most Recent Exchange-Correlation Functionals for the Large and Chemically Diverse GMTKN55 Benchmark

Benchmarks that span a broad swath of chemical space, such as GMTKN55, are very useful for assessing progress in the quest for more universal DFT functionals. We find that the WTMAD2 metrics for a great number of functionals show a clear "Jacob's Ladder hierarchy"; that the "combinatorial" development strategy of Head-Gordon and coworkers generates "best on rung" performers; that the quality of the nonlocal dispersion correction becomes more important as functionals become more accurate for nondispersion properties; that fitting against small, unrepresentative benchmark sets leads to underperforming functionals; and that {\omega}B97M(2) is currently the best DFT functional of any kind, but that revDSD-D4 functionals are able to reach similar performance using fewer parameters, and that revDOD-D4 in addition permits reduced-scaling algorithms. If one seeks a range-separated hybrid (RSH) GGA that also performs well for optical excitation energies, CAM-QTP-01 may be a viable option. The D4 dispersion model, with its partial charge dependence, appears to be clearly superior to D3BJ and even possibly NL. Should one require a double hybrid without dispersion model, noDispSD-SCAN is a viable option. Performance for the MOBH35 transition metal benchmark is different: the best double hybrids are competitive but not superior to {\omega}B97M-V, which offers the best performance compromise for mixed main group-transition metal problems.Comment: 5 pages (ICCMSE-2019 conference proceedings), AIP Conference Proceedings, in pres

Assessment of W1 and W2 theories for the computation of electron affinities, ionization potentials, heats of formation, and proton affinities

The performance of two recent {\em ab initio} computational thermochemistry schemes, W1 and W2 theory [J.M.L. Martin and G. de Oliveira, J. Chem. Phys. 111, 1843 (1999}], is assessed for an enlarged sample of thermochemical data consisting of the ionization potentials and electron affinities in the G2-1 and G2-2 sets, as well as the heats of formation in the G2-1 and a subset of the G2-2 set. We find W1 theory to be several times more accurate for ionization potentials and electron affinities than commonly used (and less expensive) computational thermochemistry schemes such as G2, G3, and CBS-QB3: W2 theory represents a slight improvement for electron affinities but no significant one for ionization potentials. The use of a two-point $A+B/L^5$ rather than a three-point $A+B/C^L$ extrapolation for the SCF component greatly enhances the numerical stability of the W1 method for systems with slow basis set convergence. Inclusion of first-order spin-orbit coupling is essential for accurate ionization potentials and electron affinities involving degenerate electronic states: inner-shell correlation is somewhat more important for ionization potentials than for electron affinities, while scalar relativistic effects are required for the highest accuracy. The mean deviation from experiment for the G2-1 heats of formation is within the average experimental uncertainty. W1 theory appears to be a valuable tool for obtaining benchmark quality proton affinities.Comment: Journal of Chemical Physics, in press (303115JCP). 2 RevTeX files, first is text and tables, second is E-PAPS tables S-1 through S-5. Additional supplementary material (total energies, basis function exponents) available at http://theochem.weizmann.ac.il/web/papers/w1w2.htm

A bilayer Double Semion Model with Symmetry-Enriched Topological Order

We construct a new model of two-dimensional quantum spin systems that combines intrinsic topo- logical orders and a global symmetry called flavour symmetry. It is referred as the bilayer Doubled Semion model (bDS) and is an instance of symmetry-enriched topological order. A honeycomb bi- layer lattice is introduced to combine a Double Semion Topolgical Order with a global spin-flavour symmetry to get the fractionalization of its quasiparticles. The bDS model exhibits non-trival braid- ing self-statistics of excitations and its dual model constitutes a Symmetry-Protected Topological Order with novel edge states. This dual model gives rise to a bilayer Non-Trivial Paramagnet that is invariant under the flavour symmetry and the well-known spin flip symmetry.Comment: revtex4 file, color figure

Fully ab initio atomization energy of benzene via W2 theory

The total atomization energy at absolute zero, (TAE$_0$) of benzene, C$_6$H$_6$, was computed fully {\em ab initio} by means of W2h theory as 1306.6 kcal/mol, to be compared with the experimentally derived value 1305.7+/-0.7 kcal/mol. The computed result includes contributions from inner-shell correlation (7.1 kcal/mol), scalar relativistic effects (-1.0 kcal/mol), atomic spin-orbit splitting (-0.5 kcal/mol), and the anharmonic zero-point vibrational energy (62.1 kcal/mol). The largest-scale calculations involved are CCSD/cc-pV5Z and CCSD(T)/cc-pVQZ; basis set extrapolations account for 6.3 kcal/mol of the final result. Performance of more approximate methods has been analyzed. Our results suggest that, even for systems the size of benzene, chemically accurate molecular atomization energies can be obtained from fully first-principles calculations, without resorting to corrections or parameters derived from experiment.Comment: J. Chem. Phys., accepted. RevTeX, 12 page

A definitive heat of vaporization of silicon through benchmark ab initio calculations on SiF_4

In order to resolve a significant uncertainty in the heat of vaporization of silicon -- a fundamental parameter in gas-phase thermochemistry -- $\Delta H^\circ_{f,0}$[Si(g)] has been determined from a thermochemical cycle involving the precisely known experimental heats of formation of SiF_4(g) and F(g) and a benchmark calculation of the total atomization energy (TAE_0) of SiF_4 using coupled-cluster methods. Basis sets up to $[8s7p6d4f2g1h]$ on Si and $[7s6p5d4f3g2h]$ on F have been employed, and extrapolations for residual basis set incompleteness applied. The contributions of inner-shell correlation (-0.08 kcal/mol), scalar relativistic effects (-1.88 kcal/mol), atomic spin-orbit splitting (-1.97 kcal/mol), and anharmonicity in the zero-point energy (+0.04 kcal/mol) have all been explicitly accounted for. Our benchmark TAE_0=565.89 \pm 0.22 kcal/mol leads to $\Delta H^\circ_{f,0}$[Si(g)]=107.15 \pm 0.38 kcal/mol ($\Delta H^\circ_{f,298}$[Si(g)]=108.19 \pm 0.38 kcal/mol): between the JANAF/CODATA value of 106.5 \pm 1.9 kcal/mol and the revised value proposed by Grev and Schaefer [J. Chem. Phys. 97, 8389 (1992}], 108.1 \pm 0.5 kcal/mol. The revision will be relevant for future computational studies on heats of formation of silicon compounds.Comment: J. Phys. Chem. A, submitted Feb 1, 199