PYSCF is a Python-based general-purpose electronic structure platform that both supports first-principles simulations of molecules and solids, as well as accelerates the development of new methodology and complex computational workflows. The present paper explains the design and philosophy behind PYSCF that enables it to meet these twin objectives. With several case studies, we show how users can easily implement their own methods using PYSCF as a development environment. We then summarize the capabilities of PYSCF for molecular and solid-state simulations. Finally, we describe the growing ecosystem of projects that use PYSCF across the domains of quantum chemistry, materials science, machine learning and quantum information science.

A review of hysteresis models for soil-water characteristic curves is presented. The models can be categorized into two groups: (i) domain models (or physically based models) and (ii) empirical models. Some models are capable of predicting scanning curves, while other models are capable of predicting the boundary wetting curve and the boundary drying curve. A comparison of the ability of five selected models to predict the boundary wetting curve showed that the Feng and Fredlund model with enhancements by Pham, Fredlund, and Barbour appears to be the most appropriate model for engineering practice. Another comparison among five physically based models for predicting scanning curves showed that the Mualem model-II gives the best overall prediction of scanning curves. The study showed that taking the effect of pore blockage into account does not always give a better prediction of hysteretic soil-water characteristic curves. A scaling method for estimating the initial drying curve, the boundary wetting curve, and the boundary drying curve is also presented in the paper.Key words: soil-water characteristic curve, hysteresis model, comparison, boundary curve, scanning curve, unsaturated soils.

Density matrix embedding theory (DMET) [ Phys. Rev. Lett. 2012, 109, 186404] has been demonstrated as an efficient wave-function-based embedding method to treat extended systems. Despite its success in many quantum lattice models, the extension of DMET to real chemical systems has been tested only on selected cases. Herein, we introduce the use of the complete active space self-consistent field (CASSCF) method as a correlated impurity solver for DMET, leading to a method called CAS-DMET. We test its performance in describing the dissociation of H-H single bonds in a H ring model system and an N═N double bond in azomethane (CH-N═N-CH) and pentyldiazene (CH(CH)-N═NH). We find that the performance of CAS-DMET is comparable to CASSCF with different active space choices when single-embedding DMET corresponding to only one embedding problem for the system is used. When multiple embedding problems are used for the system, the CAS-DMET is in good agreement with CASSCF for the geometries around the equilibrium, but not in equal agreement at bond dissociation.

A systematic investigation on electronic band structure of a series of isoreticular metal−organic frameworks (IRMOFs) using density functional theory has been carried out. Our results show that halogen atoms can be used as functional groups to tune not only the band gap but also the valence band maximum (VBM) in MOFs. Among halogen atoms (F, Cl, Br, I), iodine is the best candidate to reduce the band gap and increase the VBM value. In addition, it has been found that for the antiaromatic linker DHPDC (1,4-dihydropentalene-2,5-dicarboxylic acid) the energy gap is 0.95 eV, which is even lower than those calculated for other aromatic linkers, i.e., FFDC (furo[3,2-b]furan-2,5-dicarboxylic acid) and TTDC (thieno[3,2-b]thiophene-2,5-dicarboxylic acid). By analyzing the lowest unoccupied molecular orbital−highest occupied molecular orbital gaps calculated at the molecular level, we have highlighted the important role of the corresponding organic linkers in the MOF band gap. In particular, the change of C−C−CO dihedral angle in the organic linker can be used to analyze the difference of band gaps in MOF crystals. It is shown that a deep understanding of chemical bonding within linker molecules from electronic structure calculations plays a crucial role in designing semiconductor properties of MOF materials for engineering applications.