MrPIXEL

MrPIXEL analyzes crystal packing energetics by performing automated PIXEL calculations to quantify intermolecular interaction energies and lattice energies from crystal structure information.

Key Features:

• Semi-Empirical PIXEL Method: Represents molecules as blocks of undistorted ab initio molecular electron and nuclear densities subdivided into small volume elements (pixels) and calculates electrostatic, polarization, dispersion, and Pauli repulsion terms between pixel pairs and nuclei across molecules.
• Automated Workflow: Automates PIXEL calculation steps including atom-type assignment, input file generation, electron-density calculation submission, and result retrieval.
• Integration with CSD: Integrates with the CSD Python API to access crystallographic data and to enable local or remote execution of electron-density and PIXEL calculations.
• Comprehensive Energy Calculations: Computes full lattice energies for structures with up to two molecules in the crystallographic asymmetric unit and reports molecule–molecule interaction energies for more complex cases.

Scientific Applications:

• Phase Stability and Polymorphism: Quantifies intermolecular interaction energies to support quantitative thermodynamic rationalization of phase stability and polymorphism.
• Physical and Chemical Property Insights: Provides energetic insights into properties such as solubility, compressibility, and host–guest formation.

Methodology:

MrPIXEL uses a two-module procedure: the first module assigns atom types and prepares input files from the crystallographic model; the second module performs ab initio electron-density calculations (locally or remotely), retrieves results, and executes PIXEL calculations that subdivide molecular electron and nuclear densities into pixels and compute electrostatic, polarization, dispersion, and Pauli repulsion terms between pixels and nuclei.