The effective fragments are rigid and their potentials are generated from a set of ab initio calculations on each unique isolated fragment. The EFP includes: () multipoles (produced by the Stone’s Distributed Multipolar Analysis) for Coulomb and polarization terms; () static polarizability tensors centered at localized molecular orbital (LMO) centroids (obtained from coupled-perturbed Hartree-Fock calculations), which are used for calculations of polarization; () dynamic polarizability tensors centered on the LMOs that are generated by time-dependent HF calculations and used for calculations of dispersion; and () the Fock matrix, basis set, and localized orbitals needed for the exchange-repulsion term. Additionally, the EF potential contains coordinates of atoms, coordinates of the points of multi-polar expansion (typically, atoms and bond mid-points), coordinates of the LMO centroids, electrostatic and polarization screening parameters, and atomic labels of the EF atoms.
Q-Chem provides a library of standard fragments with precomputed effective fragment potentials. Currently the library includes common organic solvents, nucleobases, and molecules from S22 and S66 datasets for non-covalent interactions; see Table 11.8. EFP potentials in gamess format are supported by new EFPMAN2 module. They are stored in $QCAUX/fraglib directory.
|guanine enol N7||GUANINE_EN7_L|
|guanine enol N9||GUANINE_EN9_L|
|guanine enol N9RN7||GUANINE_EN9RN7_L|
|guanine keton N7||GUANINE_KN7_L|
|guanine keton N9||GUANINE_KN9_L|
|acetamide, S66, gas phase||ACETAMIDE_L|
|acetamide, S66, H-bonded dimer||ACETAMIDE_HB_L|
|acetic acid, S66, gas phase||ACETICAC_L|
|acetic acid, S66, H-bonded dimer||ACETICAC_HB_L|
|adenine, S22 stack dimer||ADENINE_L|
|adenine, S22 WC dimer||ADENINE_WC_L|
|formic acid, S22 H-bonded dimer||FORMICAC_HB_L|
|formamide, S22 dimer||FORMID_L|
|thymine, S22 stack dimer||THYMINE_L|
|thymine, S22 WC dimer||THYMINE_WC_L|
|uracil, S66, gas phase||URACIL_L|
|uracil, S66, H-bonded dimer||URACIL_HB_L|
Note: The fragments from Q-Chem fragment library have _L added to their names to distinguish them from user-defined fragments.
The parameters for the standard fragments were computed as follows. The geometries of the solvent molecules were optimized by MP2/cc-pVTZ; geometries of nucleobases were optimized with RI-MP2/cc-pVTZ. Geometries of molecules from S22 and S66 datasets are discussed in Ref. Flick:2012. The EFP parameters were obtained in gamess. To generate the electrostatic multipoles and electrostatic screening parameters, analytic DMA procedure was used, with 6-31+G* basis for non-aromatic compounds and 6-31G* for aromatic compounds and nucleobases. The rest of the potential, i.e., static and dynamic polarizability tensors, wave function, Fock matrix, etc., were obtained using 6-311++G(3df,2p) basis set.