Professor Joachim Sauer
Quantum Chemist and Professor Emeritus of Physical and Theoretical Chemistry at the Humboldt University of Berlin
Ab Initio Free Energy Predictions with Chemical Accuracy: Adsorption and Catalysis in Nanoporous Materials
The rational design of improved nanoporous materials requires the reliable prediction of rate and equilibrium constants, i.e. free energies, for elementary reaction and adsorption/desorption steps with no other input than the atomic positions. For realistic molecule-surface interaction models with hundreds of atoms in the simulation cell, with an accuracy that is comparable to experiment, this is a challenging problem of computational quantum chemistry.
We present a general ab initio divide-and-conquer approach that uses (i) hybrid high-level QM (reaction site):low level QM (periodic solid) energies for stationary points (QM – quantum mechanics) and (ii) anharmonic partition functions for local sampling of the potential energy surface (PES).
We show that chemical accuracy (±4 kJ/mol) is reached for elementary reaction steps in zeolites and for adsorption in
zeolites and MOFs. For global sampling of the PES we use lattice models. For example, for adsorption of CO2, CH4, N2, CO, in MOFs, chemically accurate free energies for adsorption on individual sites serve as input for Grand Canonical Monte Carlo lattice simulations for gas-mixture isotherms and adsorption selectivities.