Calculation of molecular thermodynamic quantities is one of the most frequently involved task in daily quantum chemistry studies. In this article, we present a general, stand-alone, powerful and flexible code named Shermo for calculating various common thermochemistry data. This code is compatible with Gaussian, ORCA, GAMESS-US and NWChem and has many unique advantages: the output information is very easy to comprehend; thermodynamic quantities can be fully decomposed to contributions of various sources; temperature and pressure can be conveniently scanned; two quasi-rigid-rotor harmonic oscillator (quasi-RRHO) models are supported to properly deal with low frequencies; different frequency scale factors can be simultaneously specified for calculating different thermodynamic quantities; conformation weighted thermodynamic data can be directly evaluated; the code can be easily run and embedded into shell script. We hope the Shermo program will bring great convenience to quantum chemists. This code can be freely obtained at http://sobereva.com/soft/shermo.

The independent gradient model (IGM) originally proposed in Phys. Chem. Chem. Phys., 19, 17928 (2017) has been increasingly popular in visual analysis of intramolecular and intermolecular interactions in recent years, and it has many clear advantages over the widely employed noncovalent interaction (NCI) method, such as intrafragment and interfragment interactions can be elegantly isolated and thus separately studied, the isosurfaces are smoother and less jaggy. However, we frequently observed that there is an evident shortcoming of IGM map in graphically studying weak interactions, that is its isosurfaces are usually too bulgy; in these cases, not only the graphical effect is poor, but also the color on some areas on the isosurfaces is inappropriate and may lead to erroneous analysis conclusions. In addition, the IGM method was originally proposed based on promolecular density, which is quite crude and does not take actual electronic structure into account. In this article, we first present a detailed overview of the IGM analysis, and then propose our new variant of IGM, namely IGM based on Hirshfeld partition of molecular density (IGMH), which replaces the free-state atomic densities involved in the IGM method with the atomic densities derived by Hirshfeld partition of actual molecular electron density. This change makes IGM have more rigorous physical background. In addition, we describe some indices defined on the top of IGM or IGMH framework to quantify contributions from various atoms or atom pairs to interaction between specific fragments. A large number of application examples in this article, including molecular and periodic systems, weak and chemical bond interactions, fully demonstrate the important value of IGMH in intuitively understanding interactions in chemical systems. Comparisons also showed that the IGMH usually has markedly better graphical effect than IGM and overcomes known problems in IGM. Currently IGMH analysis has been efficiently supported in our freely available and user-friendly wavefunction analysis code Multiwfn (http://sobereva.com/multiwfn), and a detailed tutorial is presented. We hope that IGMH will become a new popular method among chemists for exploring interactions in wide variety of chemical systems.