Reliable crystal structure predictions from first principles

Abstract

An inexpensive and reliable method for molecular crystal structure predictions (CSPs) has been developed. The new CSP protocol starts from a two-dimensional graph of crystal’s monomer(s) and utilizes no experimental information. Using results of quantum mechanical calculations for molecular dimers, an accurate two-body, rigid-monomer ab initio-based force field (aiFF) for the crystal is developed. Since CSPs with aiFFs are essentially as expensive as with empirical FFs, tens of thousands of plausible polymorphs generated by the crystal packing procedures can be optimized. Here we show the robustness of this protocol which found the experimental crystal within the 20 most stable predicted polymorphs for each of the 15 investigated molecules. The ranking was further refined by performing periodic density-functional theory (DFT) plus dispersion correction (pDFT+D) calculations for these 20 top-ranked polymorphs, resulting in the experimental crystal ranked as number one for all the systems studied (and the second polymorph, if known, ranked in the top few). Alternatively, the polymorphs generated can be used to improve aiFFs, which also leads to rank one predictions. The proposed CSP protocol should result in aiFFs replacing empirical FFs in CSP research.

Crystal Structure Predictions for 4-Amino-2,3,6-trinitrophenol Using a Tailor-Made First-Principles-Based Force Field

“…For example, there is a fairly large discrepancy between the fit and the ab initio value of the interaction energy at minimum number 4 (see Table ). A method for resolving this problem was proposed in ref . It consists of computing SAPT­(DFT) interaction energies for additional grid points generated by near-neighbor dimers selected from a number of top-ranked polymorphs predicted with an initial version of the force field.…”

“…During the generation step, rigid molecules may be randomly placed with interatomic distances smaller than the repulsive wall of the SAPT­(DFT) potential, so the unit cells are first optimized using a combination of the standard OPLS-AA Lennard-Jones parametrization and the SAPT­(DFT) fitted charges to avoid ending up in holes in the potential (the A 12 ab /( r ab ) 12 terms greatly reduce the severity of holes, but do not remove them completely). The final 0 K optimization uses the full SAPT­(DFT) rigid-monomer intermolecular potential and hole-fixing procedure and a modified version of UPACK . These energies are used to rank the possible rigid molecule structures.…”

“…The final 0 K optimization uses the full SAPT(DFT) rigid-monomer intermolecular potential and hole-fixing procedure and a modified version of UPACK. 77 These energies are used to rank the possible rigid molecule structures.…”

Efficient Crystal Structure Prediction for Structurally Related Molecules with Accurate and Transferable Tailor-Made Force Fields

“…Modest restraints pulling multipole moments to zero are used to alleviate ambiguities related to buried atoms. Atomic polarizability , is not explicitly considered; however, it is possible that the off-diagonal terms of the van der Waals parameters capture the polarization effects to a certain extent.…”

A semiempirical potential for alkali halide diatoms with damped interactions I. Rittner potential

“…We are not aware of formal calculations of the damping of the Coulomb potential with which to compare eqn (5) although it has been adopted at least in one other publication. 42 In a related problem Stone in his book The Theory of Intermolecular Forces has calculated the correction of the electrostatic multipole energy at short distances, which he denotes the “penetration energy”. 43 Accordingly, the energy of a proton as a function of distance from a hydrogen-like atom of nuclear charge Z is given by: V ( R ) = −1/2[1 − exp(−2 ZR )(1 + RZ )], where the term in brackets is the damping function and exp(−2 ZR ) is the charge density of the atom.…”