Behavior of density functionals with respect to basis set. VI. Truncation of the correlation consistent basis sets

Correlation consistent basis sets designed for density functional theory: Third-row atoms (Ga-Br)

The correlation consistent basis sets (cc-pVnZ with n = D, T, Q, 5) for the Ga-Br elements have been redesigned, tuning the sets for use for density functional approximations. Steps to redesign these basis sets for an improved correlation energy recovery and efficiency include truncation of higher angular momentum functions, recontraction of basis set coefficients, and reoptimization of basis set exponents. These redesigned basis sets are compared with conventional cc-pVnZ basis sets and other basis sets, which are, in principle, designed to achieve systematic improvement with respect to increasing basis set size. The convergence of atomic energies, bond lengths, bond dissociation energies, and enthalpies of formation to the Kohn-Sham limit is improved relative to other basis sets where convergence to the Kohn-Sham limit is typically not observed.

Assessment of DFT for endohedral complexes' dipole moment: PNO-LCCSD-F12 as a reference method

We present a systematic evaluation of the performance of a wide range of exchange-correlation functionals and related dispersion correction schemes for the computation of dipole moments of endohedral complexes, formed through the encapsulation of an AB molecule (AB = LiF, HCl) inside carbon nanotubes (CNTs) of different diameter. The consistency and accuracy of (i) generalized gradient approximation, (ii) meta GGA, (iii) global hybrid, and (iv) range-separated hybrid density functionals are assessed. In total, 37 density functionals are tested. The results obtained using the highly accurate pair natural orbitals based explicitly correlated local coupled cluster singles doubles (PNO-LCCSD-F12) method of Werner and co-workers [Schwilk et al., J. Chem. Theory Comput., 2017, 13, 3650; Ma et al., J. Chem. Theory Comput., 2017, 13, 4871] with the aug-cc-pVTZ basis set serve as a reference. The static electric dipole moment is computed via the finite field response or, when possible, as the expectation value of the dipole operator. Among others, it is shown that functionals belonging to the class of range-separated hybrids, provide results closest to the coupled cluster reference data. In particular, the ωB97X as well as the M11 functional may be considered as a promising choice for computing electric properties of noncovalent endohedral complexes. On the other hand, the worst performance was found for the functionals which do not include the Hartree-Fock exchange. The analysis of both the coupled cluster and the DFT results indicates a strong coupling of dispersion and polarization that may also explain why lower level DFT methods, as well as Hartree-Fock and MP2, cannot yield dipole moments beyond a qualitative agreement with the higher order reference data. Interestingly, the much smaller and less systematically constructed basis sets of Pople of moderate size provide results of accuracy at least comparable with the extended Dunning's aug-cc-pVTZ basis set.

Computational modelling of singlet excitation energy transfer: a DFT/TD-DFT study of the ground and excited state properties of a syn bimane dimer system using non-empirically tuned range-separated functionals

Range-tuned DFT/TD-DFT improves predicted properties for the sequence of events leading to excitation energy transfer (EET) in bimanes.

Partition coefficients for the SAMPL5 challenge using transfer free energies

SAMPL challenges (Mobley et al. in J Comput Aided Mol Des 28:135-150, 2014; Skillman in J Comput Aided Mol Des 26:473-474, 2012; Geballe in J Comput Aided Mol Des 24:259-279, 2010; Guthrie in J Phys Chem B 113:4501-4507, 2009) provide excellent opportunities to assess theoretical approaches on new data sets with a goal of gaining greater insight towards protein and ligand modeling. In the SAMPL5 experiment, cyclohexane-water partition coefficients were determined using a vertical solvation scheme in conjunction with the SMD continuum solvent model. Several DFT functionals partnered with correlation consistent basis sets were evaluated for the prediction of the partition coefficients. The approach chosen for the competition, a B3PW91 vertical solvation scheme, yields a mean absolute deviation of 1.9 logP units and performs well at estimating the correct hydrophilicity and hydrophobicity for the full SAMPL5 molecule set.

Efficient Diffuse Basis Sets: cc-pVxZ+ and maug-cc-pVxZ

We combine the diffuse basis functions from the 6-31+G basis set of Pople and co-workers with the correlation-consistent basis sets of Dunning and co-workers. In both wave function and density functional calculations, the resulting basis sets reduce the basis set superposition error almost as much as the augmented correlation-consistent basis sets, although they are much smaller. In addition, in density functional calculations the new basis sets, called cc-pVxZ+ where x = D, T, Q, ..., or x = D+d, T+d, Q+d, ..., give very similar energetic predictions to the much larger aug-cc-pVxZ basis sets. However, energetics calculated from correlated wave function calculations are more slowly convergent with respect to the addition of diffuse functions. We also examined basis sets with the same number and type of functions as the cc-pVxZ+ sets but using the diffuse exponents of the aug-cc-pVxZ basis sets and found very similar performance to cc-pVxZ+; these basis sets are called minimally augmented cc-pVxZ, which we abbreviate as maug-cc-pVxZ.

Modeling the photophysics of Zn and Cd monomers, metallophilic dimers, and covalent excimers

Density functional (Xα, BLYP, BPW91, B3LYP, and B3PW91), MP2, and coupled cluster with singles, doubles, and quasiperturbative triple excitations (CCSD(T)) methods in combination with LANL2DZ, cc-pVxZ, cc-pVxZ-PP, or cc-pVxZ-DK (where x = D (double), T (triple) Q (quadruple), and 5 (quintuple)) basis sets have been employed in computations of excited states of zinc and cadmium dimers and monomers. The spectroscopic constants r(e), D(e), T(e), ω(e), ω(e)x(e), and B(e) are compared among group 12 dimers in their ground and low-lying phosphorescent excited states. The weak metallophilic bonding in the ground state requires MP2 or CCSD(T) description, whereas the excimeric bonding is well described by CCSD(T), BLYP, B3LYP, BPW91, and B3PW91. Consistent with our previous work on Hg(n) species, absorption and phosphorescence transition energies that agree well with experimental results can be obtained with CCSD(T) and B3PW91 methods in combination with the correlation consistent basis sets of triple-ζ or higher level. This is the case for monomers and *Cd(2) and *Zn(2) lowest triplet excimers (in either the (3)Σ(u)(+) or (3)Π(g) state). The CCSD(T)/aug-cc-pV5Z-PP combination results in values that are only 150 and 240 cm(-1) (<1% errors) removed from the experimental values for the (1)S → (3)D atomic transitions for Zn and Cd, respectively. Such spectroscopic constants provide the most accurate theoretical values known to date for bonding and photophysical parameters characteristic of Zn(n) and Cd(n) species.

How reliable are DFT transition structures? Comparison of GGA, hybrid-meta-GGA and meta-GGA functionals

There have been many comparisons of computational methods applied to ground states, but studies of organic reactions usually require calculations on transition states, and these provide a different test of the methods. We present calculations of the geometries of nineteen covalent-bond forming transition states using HF and twelve different functionals, including GGA, hybrid-GGA and hybrid meta-GGA approaches. For the calculation of the TS geometries, the results suggest that B3LYP is only slightly less accurate than newer, computationally more expensive methods, and is less sensitive to choice of integration grid. We conclude that the use of B3LYP and related functionals is still appropriate for many studies of organic reaction mechanisms.

Exploration of density functional methods for one-electron reduction potential of nitrobenzenes

Performance of the set of density functional approaches for calculation of one-electron reduction potentials of nitroaromatic compounds was investigated. To select the most precise and affordable method, we selected a set of model molecules and investigated effects of basis set, density functional, and solvation model on the calculation of reduction potentials. It was found that the mPWB1K/TZVP method provides the most accurate gas phase electron affinity values (RMS error is 0.1 eV). This method in conjunction with the PCM (Bondi) method yields also the most accurate difference in solvation energies of neutral oxidized form and anion-radical reduced form. The final E0 values were calculated with RMS error of 0.10 V, compared with experimental values.

Complete basis set B3LYP NMR calculations of CDCl3 solvent's water fine spectral details

The assignment of singlet at 1.55 ppm and the 1:1:1 triplet at 1.519 ppm to H(2)O and HOD in the 400 MHz (1)H NMR spectrum of CDCl(3) solvent were supported by complete basis set (CBS) GIAO-B3LYP calculated chemical shift and the CBS B3LYP estimated (2)J(D,H) spin-spin coupling constant (SSCC). The CBS fitting of B3LYP/cc-pCVxZ and B3LYP/pcJ-n predicted SSCC values, the accurate value of (2)J(D,H) = -1.082 +/- 0.030 Hz of HOD in chloroform-d(1) and the H/D isotopic shift of 0.0307(1) ppm were reported for the first time. The agreement between CBS B3LYP predicted chemical shift, spin-spin values and experiment was good.