Assessment of Perturbative Explicitly Correlated Methods for Prototypes of Multiconfiguration Electronic Structure

The performance of the [2]_S and [2]_R12 universal perturbative corrections that account for one- and many-body basis set errors of single- and multiconfiguration electronic structure methods is assessed. A new formulation of the [2]_R12 methods is used in which only strongly occupied orbitals are correlated, making the approach more amenable for larger computations. Three model problems are considered using the aug-cc-pVXZ (X = D,T,Q) basis sets: the electron affinity of fluorine atom, a conformational analysis of two Si₂H₄ structures, and a description of the potential energy surfaces of the X ¹Σ_g⁺, a ³Π_u, b ³Σ_g^‑, and A ¹Π_u states of C₂. In general, the [2]_R12 and [2]_S corrections enhance energy convergence for conventional multireference configuration interaction (MRCI) and multireference perturbation theory (MRMP2) calculations compared to their complete basis set limits. For the electron affinity of the F atom, [2]_R12 electron affinities are within 0.001 eV of the experimental value. The [2]_R12 conformer relative energy error for Si₂H₄ is less than 0.1 kcal/mol compared to the complete basis set limit. The C₂ potential energy surfaces show nonparallelity errors that are within 0.7 kcal/mol compared to the complete basis set limit. The perturbative nature of the [2]_R12 and [2]_S methods facilitates the development of a straightforward text-based data exchange standard that connects an electronic structure code that can produce a two-particle density matrix with a code that computes the corrections. This data exchange standard was used to implement the interface between the GAMESS MRCI and MRMP2 codes and the MPQC [2]_R12 and [2]_S capabilities

Spin-Free [2]_R12 Basis Set Incompleteness Correction to the Local Multireference Configuration Interaction and the Local Multireference Average Coupled Pair Functional Methods

The local multireference configuration interaction (LMRCI) and local multireference averaged coupled pair functional (LMRACPF) methods are extended to include explicit correlation via the universal spin-free [2]_R12 basis set incompleteness correction. Four test cases are examined to measure the performance of the LMRCI+[2]_R12 (without and with the Davidson + Q correction for size-extensivity) and LMRACPF+[2]_R12 methods. These tests examine bond dissociation energies (BDEs) for ethene, perfluoroethene, propene, and 2-butene. As has been demonstrated for other methods, the LMRCI+[2]_R12/LMRCI+Q+[2]_R12/LMRACPF+[2]_R12 BDEs are as accurate as the conventional LMRCI/LMRACPF BDEs that are computed with the basis set one cardinal number higher. It is shown that LMRCI+[2]_R12/LMRCI+Q+[2]_R12/LMRACPF+[2]_R12 BDEs computed with the June calendar basis sets preserve the accuracy of the corresponding BDEs computed with the conventional aug-cc-pVXZ basis sets (where X = D, T, Q)

Reading Genesis–Joshua as a Unified Document from an Early Date: A Settler Colonial Perspective

This essay proposes based on literary-compositional considerations how two authors working together could have composed Genesis–Joshua. After this, it suggests that Genesis–Joshua can be seen to reflect a sociopolitical transformation of ancient Canaanite societies into an Israelite one(s) through a process that can be labeled as ancient settler colonialism, and that the document could have been written concomitantly. Subsequently, relevant ancient Near Eastern and archaeological evidence will be considered, suggesting compatibility with the idea that Genesis–Joshua has reused and readapted existing traditions together with creative narrative retelling for its socio-political purposes, and that this could have already taken place from the late second millennium Bce on. The essay concludes by drawing out some explicit contemporary implications of such a reading of Genesis–Joshua