Zdzisław Latajka

Application of density functional methods for the study of hydrogen‐bonded systems: The hydrogen fluoride dimer

Systematic studies of the ability of a broad family of density functional methods applied to hydrogen‐bonded complexes have been carried out on the hydrogen fluoride dimer. Specifically, calculations have been performed using basis sets of triple‐zeta quality with diffuse functions and multiple sets of polarization functions. Various local and nonlocal exchange‐correlation functionals have been applied in order to study the structure, energetics, and vibrational properties of the hydrogen fluoride dimer. The comparison with the experimental data, and also with results coming from ab initio methods (Hartree–Fock, Mo/ller–Plesset second order, and quadratic configuration interaction with the single and double excitations) shows good performance of nonlocal density functional methods for the description of hydrogen‐bonded systems. The calculated binding energy, with nonlocal Becke exchange and Lee–Yang–Parr correlation functionals and a 6‐311++G(3df,3pd) basis set, is 4.48 kcal/mol and is in good agreement w...

Structure, Energetics, and Vibrational Spectra of H-Bonded Systems. Dimers and Trimers of HF and HCl

Abstract The title complexes are studied by ab initio methods using double-ζ basis sets augmented by diffuse sp and two sets of polarization functions. The binding energies decrease in the order (HF) 2 > HF…HCl > (HCl) 2 , all of which form pseudolinear H bonds. While not important for (HF) 2 , correlation plays an increasingly larger role as each HF is replaced by HCl, contributing 2 3 of the total binding energy of (HCl) 2 . (HF) 3 and (HCl) 3 are both C 3h cyclic and exhibit cooperativity, particularly (HF) 3 ; correlation appears to be negligible in the three-body nonadditive interaction energies. The red shift of the HF stretch in (HF) 3 is nearly twice as great as in the dimer while little enhancement is observed in the HCl analogues. The other two observable bands in the trimers are of fairly high intensity and correspond to an out-of-plane and in-plane bend. The intermolecular stretching modes in the dimers and trimers are of very low intensity. A clear relationship is noted between the intermolecular frequencies and the strength of the interaction.

Theoretical infrared spectrum and revised assignment for para-nitrophenol. Density functional theory studies

The harmonic vibrational frequencies and infrared intensities of p-nitrophenol as well as geometries of ortho- and para-nitrophenol, are calculated with density functional theory (DFT), using BLYP functional and 6-31G(d,p) basis set. The calculated (unscaled) spectra are in very good agreement with the gas phase and solid IR spectra of p-nitrophenol. A detailed interpretation of the infrared spectra of p-nitrophenol is reported on the basis of the calculated potential energy distribution (PED). Several reassignments have been made.

Effects of basis set and electron correlation on the calculated properties of the ammonia dimer

Ab initio calculations are carried out for (NH3)2 with a 6‐31G**(1p,2d) basis set containing diffuse polarization functions. Electron correlation is included via second‐order Mo/ller–Plesset perturbation theory (MP2). At the SCF level, the equilibrium R(NN) distance is 3.54 A and the interaction energy is −2.35 kcal/mol. Inclusion of correlation enhances the attraction substantially, increasing the energy to −4.05 kcal/mol and reducing the intermolecular separation by 0.20 A. Comparison with previous results at the SCF level demonstrates a variety of errors including exaggerated dipole moments, underestimation of polarization energy, and sizable superposition errors with these smaller basis sets.

Density functional theory applied to proton-transfer systems. A numerical test

Abstract The structure, interaction energy and proton-transfer features of the (H 5 O 2 + complex are determined by using a nonlocal density functional theory method developed recently by Salahub and co-workers. The results are compared to those of a high- order Moller-Plesset electron-correlation calculation. The DFT calculation predicts correctly a symmetrical configuration of the complex at the equilibrium O—O distance, and yields a correct value of the H-bonding interaction energy. For a larger O—O separation, the electronic correlation effects on the double-well proton potential curve are overestimated in the DFT approach, whereas they are well reproduced by the second-order Moller-Plesset expansion.

Reversal of the usual ν(CHD) spectral shift of haloforms in some hydrogen-bonded complexes

Abstract Infrared spectra in the region of the ν( CH D ) stretching frequency of chloroform, deuterochloroform and bromoform have been investigated in mixed systems containing such proton acceptors as carboxy, nitro and sulpho compounds. Intermolecular hydrogen bond formation is accompanied by a shift to higher wavenumbers of the absorption band of the stretching vibration ν( CH D ) of the haloform molecules, to the extent of 3–8 cm−1 in comparison with its position in CCl4 solution. This effect is the opposite to the usual occurrence of CH D bond weakening due to hydrogen bonding and could be considered as a strengthening of the CH D bond due to an increase of its s character caused by molecular deformation as a result of intermolecular forces. Quantum chemical modelling of the vibrational spectrum of the chloroform molecule demonstrates an increase in the ν(CH) wavenumber with increasing ClCH bond angle. However, calculation of the vibrational spectrum of the chloroform—nitromethane complex predicts an overall reduction of the ν(CH) wavenumber.

Ab initio comparison of H bonds and Li bonds. Complexes of LiF, LiCl, HF, and HCl with NH3

Ab initio calculations are carried out on the complexes H3N–LiF, H3N–LiCl and their analogs H3N–HF and H3N–HCl as well as the isolated subunits. Double‐zeta basis sets, augmented by two sets of polarization functions, are used in conjunction with second‐order Moller–Plesset perturbation theory (MP2) for evaluation of electron correlation effects. The Li bonds are found to be substantially stronger than their H‐bonding counterparts, due in large measure to the greater dipole moments of the LiX subunits. Correlation has a large effect on the geometry and energetics of both H‐bonded complexes, reducing the intermolecular separation and contributing between 20% and 40% to the total complexation energy. In contrast, the SCF and MP2 results for the Li bonds are nearly identical. The small net effect of correlation in these complexes is ascribed to cancellation between incorporation of dispersion and reduction of the electrostatic component. Another distinction between the two types of bonds arises from consider...

Critical assessment of density functional methods for study of proton transfer processes. (FHF)

Abstract Most variants of density functional theory (DFT) yield a proton transfer barrier in (F…H…F) − which is considerably smaller than the best correlated conventional ab initio results, with a large polarized basis set. The agreement is best for DFT methods with nonlocal exchange and correlation functionals, especially hybrid approaches which mix Hartree-Fock and optimized r (FH).

Possible gas-phase ion pairs in amine-HCl complexes. An ab initio theoretical study

Abstract Ab initio MO calculations were performed for complexes between HCl and NH 3 , CH 3 NH 2 , (CH 3 ) 2 NH and (CH 3 ) 3 N. SCF geometry optimization for the latter three complexes gives double-minimum potential surfaces, which become single- minimum surfaces when electron correlation is considered. It is proposed that (CH 3 ) 3 NHCl may be an ion pair in the gas phase.

Critical analysis of the calculated frequency shifts of hydrogen-bonded complexes

The frequency shift of the proton donor in hydrogen bonded complexes is an important quantity which enables to discuss the nature of the hydrogen bond. Calculations of frequency shifts by quantum chemical methods are usually performed within the harmonic approximation and therefore the comparison with experimental data is biased. We have investigated the importance of anharmonic corrections in the case of twelve complexes in which either FH or ClH is the proton donor. Hartree–Fock, Mo/ller–Plesset second and third order (MP2, MP3), density functional theory (DFT), and hybrid Hartree–Fock/DFT methods have been used for the calculations. It is shown that the anharmonic contribution to the frequency shift is rather method dependent. Its magnitude is usually 10%–20% of the total shift though it can be as large of ∼ 50% for (ClH)2. Once anharmonicity is taken into account, most methods tend to noticeably overestimate the frequency shifts. In the case of DFT related approaches this trend is interpreted in terms...