An official website of the United States government
The many-body expansion (MBE) is promising for the efficient, parallel computation of lattice energies in organic crystals. Very high accuracy should be achievable by employing coupled-cluster singles, doubles, and perturbative triples at the complete basis set limit [CCSD(T)/CBS] for the dimers, trimers, and potentially tetramers resulting from the MBE, but such a brute-force approach seems impractical for crystals of all but the smallest molecules. Here, we investigate hybrid or multi-level approaches that employ CCSD(T)/CBS only for the closest dimers and trimers and utilize much faster methods like Møller–Plesset perturbation theory (MP2) for more distant dimers and trimers. For trimers, MP2 is supplemented with the Axilrod–Teller–Muto (ATM) model of three-body dispersion. MP2(+ATM) is shown to be a very effective replacement for CCSD(T)/CBS for all but the closest dimers and trimers. A limited investigation of tetramers using CCSD(T)/CBS suggests that the four-body contribution is entirely negligible. The large set of CCSD(T)/CBS dimer and trimer data should be valuable in benchmarking approximate methods for molecular crystals and allows us to see that a literature estimate of the core-valence contribution of the closest dimers to the lattice energy using just MP2 was overbinding by 0.5 kJ mol−1, and an estimate of the three-body contribution from the closest trimers using the T0 approximation in local CCSD(T) was underbinding by 0.7 kJ mol−1. Our CCSD(T)/CBS best estimate of the 0 K lattice energy is −54.01 kJ mol−1, compared to an estimated experimental value of −55.3 ± 2.2 kJ mol−1.
more »
« less
This content will become publicly available on April 14, 2026
Systematic characterization of the homogeneous and heterogeneous hydrogen halide dimers
This study systematically characterizes the four homogeneous and six heterogeneous hydrogen-bonded dimers formed by hydrogen halide pairs (HX/HY where X, Y = F, Cl, Br, and I). The notation HX⋯HY indicates the direction of the hydrogen bond from the HY donor to the HX acceptor. All stationary points reported for these ten dimer systems are fully optimized utilizing the MP2 and CCSD(T) ab initio methods in conjunction with quadruple-ζ correlation-consistent basis sets augmented with diffuse functions, and their nature is verified by harmonic vibrational frequency computations. The electronic dissociation energies (De) for all ten global minima are evaluated near the CCSD(T) complete basis set (CBS) limit via extrapolation schemes. These values are 19.11, 8.32, 7.38, and 6.22 kJ mol−1 for the homogeneous dimers of HF, HCl, HBr, and HI, respectively. For the heterogeneous pairs, the lighter hydrogen halide is consistently the donor in the global minimum configuration, with De ranging from 12.23 kJ mol−1 for HCl⋯HF to 7.22 kJ mol−1 for HI⋯HBr near the CCSD(T) CBS limit. Interestingly, not all heterodimer donor/acceptor permutations correspond to minima. For example, the HCl⋯HBr configuration is identified as a local minimum at all levels of theory employed in this investigation, whereas the in-plane barrier for donor/acceptor exchange vanishes for HCl⋯HI and HBr⋯HI when larger quadruple-ζ basis sets are utilized. For the seven dimer systems containing Br and/or I, the structures, energetics, and vibrational frequencies computed using conventional valence-only electron correlation procedures are similar to those obtained using an expanded valence treatment that includes the (n − 1)d subvalence electrons associated with Br and I.
more »
« less
- Award ID(s):
- 2452726
- PAR ID:
- 10613290
- Publisher / Repository:
- AIP
- Date Published:
- Journal Name:
- The Journal of Chemical Physics
- Volume:
- 162
- Issue:
- 14
- ISSN:
- 0021-9606
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The optimized geometries, vibrational frequencies, and dissociation energies from MP2 and CCSD(T) computations with large correlation consistent basis sets are reported for (H2S)2and H2O/H2S. Anharmonic vibrational frequencies have also been computed with second‐order vibrational perturbation theory (VPT2). As such, the fundamental frequencies, overtones, and combination bands reported in this study should also provide a useful road map for future spectroscopic studies of the simple but important heterogeneous H2O/H2S dimer in which the hydrogen bond donor and acceptor can interchange, leading to two unique minima with very similar energies. Near the CCSD(T) complete basis set limit, the HOH⋯SH2configuration (H2O donor) lies only 0.2 kcal mol−1below the HSH⋯OH2structure (H2S donor). When the zero‐point vibrational energy is included, however, the latter configuration becomes slightly lower in energy than the former by <0.1 kcal mol−1. © 2018 Wiley Periodicals, Inc.more » « less
-
Hypohalous acids (HOX) are a class of molecules that play a key role in the atmospheric seasonal depletion of ozone and have the ability to form both hydrogen and halogen bonds. The interactions between the HOX monomers (X = F, Cl, Br) and water have been studied at the CCSD(T)/aug-cc-pVTZ level of theory with the spin free X2C-1e method to account for scalar relativistic effects. Focal point analysis was used to determine CCSDT(Q)/CBS dissociation energies. The anti hydrogen bonded dimers were found with interaction energies of −5.62 kcal mol −1 , −5.56 kcal mol −1 , and −4.97 kcal mol −1 for X = F, Cl, and Br, respectively. The weaker halogen bonded dimers were found to have interaction energies of −1.71 kcal mol −1 and −3.03 kcal mol −1 for X = Cl and Br, respectively. Natural bond orbital analysis and symmetry adapted perturbation theory were used to discern the nature of the halogen and hydrogen bonds and trends due to halogen substitution. The halogen bonds were determined to be weaker than the analogous hydrogen bonds in all cases but close enough in energy to be relevant, significantly more so with increasing halogen size.more » « less
-
Abstract The global minima of urea and thiourea were characterized along with other low‐lying stationary points. Each structure was optimized with the CCSD(T) method and triple‐ζcorrelation consistent basis sets followed by harmonic vibrational frequency computations. Relative energies evaluated near the complete basis set limit with both canonical and explicitly correlated CCSD(T) techniques reveal several subtle but important details about both systems. These computations resolve a discrepancy by demonstrating that the electronic energy of the C2vsecond‐order saddle point of urea lies at least 1.5 kcal mol−1above the C2global minimum regardless of whether the structures were optimized with MP2, CCSD, or CCSD(T). Additionally, urea effectively has one minimum instead of two because the electronic barrier for inversion at one amino group in the Cslocal minimum vanishes at the CCSD(T) CBS limit. Characterization of both systems with the same ab initio methods and large basis sets conclusively establishes that the electronic barriers to inversion at one or both NH2groups in thiourea are appreciably smaller than in urea. CCSDT(Q)/cc‐pVTZ computations show higher‐order electron correlation effects have little impact on the relative energies and are consistently offset by core correlation effects of opposite sign and comparable magnitude.more » « less
-
A quantitative assessment of deformation energy in intermolecular interactions: How important is it?Dimer interaction energies have been well studied in computational chemistry, but they can offer an incomplete understanding of molecular binding depending on the system. In the current study, we present a dataset of focal-point coupled-cluster interaction and deformation energies (summing to binding energies, De) of 28 organic molecular dimers. We use these highly accurate energies to evaluate ten density functional approximations for their accuracy. The best performing method (with a double-ζ basis set), B97M-D3BJ, is then used to calculate the binding energies of 104 organic dimers, and we analyze the influence of the nature and strength of interaction on deformation energies. Deformation energies can be as large as 50% of the dimer interaction energy, especially when hydrogen bonding is present. In most cases, two or more hydrogen bonds present in a dimer correspond to an interaction energy of −10 to −25 kcal mol−1, allowing a deformation energy above 1 kcal mol−1 (and up to 9.5 kcal mol−1). A lack of hydrogen bonding usually restricts the deformation energy to below 1 kcal mol−1 due to the weaker interaction energy.more » « less
