Plesset Perturbation Theory Methods Research Articles

Relativistic MR-MP Energy Levels for L-shell Ions of Iron

Abstract A comprehensive set of level energies is provided for the valence and K-vacancy states of the ions Fe xvii, Fe xviii, Fe xix, Fe xx, Fe xxi, Fe xxii, Fe xxiii, and Fe xxiv. Level energies were calculated with the relativistic Multi-Reference Møller–Plesset Perturbation Theory method (MR-MP). The data set includes level energies coming from the configurations , , , , , and , where 1 ≤ q ≤ 8, n ≤ 5, and l ≤ 3. The results have been compared with data from the National Institute of Standards and Technology (NIST) online database and with previous calculations. In general, the deviation from the NIST-recommended values is below 0.6 and 1.0 eV for valence and K-vacancy level energies, respectively. However, we identify numerous outliers among the NIST-recommended values. The extensive data set presented here greatly augments the amount of available reference level energies in the NIST database for L-shell ions of Fe, and we expect our data set to ease line identification and confirm level designations.

Theoretical investigation of cyromazine tautomerism using density functional theory and Møller–Plesset perturbation theory methods

ABSTRACTA computational chemistry analysis of six unique tautomers of cyromazine, a pesticide used for fly control, was performed with density functional theory (DFT) and canonical second-order Møller–Plesset perturbation theory (MP2) methods to gain insight into the contributions of molecular structure to detection properties. Full geometry optimisation using the 6-311++G** basis set provided energetic properties, natural charges, frontier orbitals and vibrational modes. Excitation energies were obtained using time-dependent DFT. Hydrogen location and bond order contribute significantly to the electronic properties. The common cyromazine tautomer possesses the lowest energy, highest band gap energy and highest excitation energy. B3LYP/6-31G** dynamics simulations indicate each tautomer possesses a stable structure with limited rotation about the single bonds. Tautomerisation involving intramolecular hydrogen transfer influences the natural charges of neighbouring atoms and the frontier orbital properties. The excitation energies are highly correlated with band gap energies of the frontier orbitals. The calculated infrared and Raman spectra are suitable for vibrational assignments associated with the chemical structure. The tautomeric forms of cyromazine possess similar spatial properties and significant variation in electronic properties.

Geometry optimizations with the incremental molecular fragmentation method

Nuclear energy gradients for the incremental molecular fragmentation (IMF) method presented in our previous work [Meitei OR, Heßelmann A, Molecular energies from an incremental fragmentation method, J Chem Phys 144(8):084109, 2016] have been derived. Using the second-order Møller–Plesset perturbation theory method to describe the bonded and nonbonded energy and gradient contributions and the uncorrelated Hartree–Fock method to describe the correction increment, it is shown that the IMF gradient can be easily computed by a sum of the underlying individual derivatives of the energy contributions. The performance of the method has been compared against the supermolecular method by optimizing the structures of a range of polyglycine molecules with up to 36 glycine residues in the chain. It is shown that with a sensible set of parameters used in the fragmentation the supermolecular structures can be fairly well reproduced. In a few cases the optimization with the IMF method leads to structures that differ from the supermolecular ones. It was found, however, that these are more stable geometries also on the supermolecular potential energy surface.

Trends in Two- and Three-Body Effects in Multiscale Clusters of Ionic Liquids.

Applications of higher correlated levels of ab initio theory to condensed systems require a significant amount of computational resources. The recent development of the fragment molecular orbital (FMO) approach alleviates this issue by splitting the system into individual fragments and achieves the accuracy of the method by accounting for all possible two-body and three-body interactions. In this work a comprehensive application of the FMO approach in combination with a second order of Møller-Plesset perturbation theory method, MP2, is presented for multiscale clusters of ionic liquids such as [C1mim]X, [C1mpyr]X, [C2py]X, and [NMe4]X, where X = chloride and tetrafluoroborates, BF4-, with the clusters varying in size from 4, 8, 16, to 32 ion pairs. Reliable cutoff criteria for the inclusion of two-body and three-body interactions are identified for both HF energy and MP2 correlation energy to achieve the desired accuracy of 1 kJ mol-1. The importance of two-body and three-body interactions in ionic liquids is also discussed.

Theoretical investigations of optical properties of l-arginine trifluoroacetate crystal

In order to determine the molecular dipole moment (μ), polarizability (α), and first hyperpolarizability (β) of l-arginine trifluoroacetate (LATF) crystals, a series of basis sets including polarized and diffuse functions have been employed at the framework of Hartree–Fock and second order Möller–Plesset perturbation theory methods. The MP2/6-311++G(d,p) model predicts for the converged value of in-crystal dipole moment, polarizability and first hyperpolarizability are 21.2 D, 20.0 × 10−24 esu and 50.0 × 10−31 esu, respectively. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. Electronic excitation properties are discussed within the framework of the two-level model on the basis of an orbital analysis. The coupled perturbed Hartree–Fock (CPHF) procedure yields information on the dispersion behavior of first hyperpolarizability terms. The magnitudes of the various hyperpolarizability terms which describe the various second-order nonlinear processes show the following trend: β(−2ω;ω,ω) > β(0;ω,−ω) > β(0,0,0). By using the molecular structures and the molecular first hyperpolarizability, the components of second harmonic tensor coefficient d of the crystals were evaluated by the oriented-gas model.

Hydrogen adsorption on C3H3–TM (TM = Sc, Ti) organometallic compounds

This work reports hydrogen adsorption on C3H3–TM (TM = Sc, Ti) organometallic compounds using second-order Moller–Plesset perturbation theory method. Two types of organometallic compounds are considered viz. transition metal-capped and transition metal-inserted. Maximum five and four hydrogen molecules were adsorbed on Sc-capped ScC3H3 and Ti-capped TiC3H3 complexes, thereby giving gravimetric hydrogen uptake capacity of 10.71 and 8.5 wt%, respectively. The gravimetric H2 uptake capacity 10.71 wt% of ScC3H3 complex is higher by 1.41 wt% than that of Sc-capped ScC4H4 organometallic complex reported earlier. The hydrogen uptake capacity 8.5 wt% of TiC3H3 is in between the uptake capacity of 6.61 and 9.1 wt% shown by Ti-capped TiC5H5 and TiC4H4 organometallic complexes, respectively. The Sc-capped and Sc-inserted ScC3H3 adsorb same number of H2 molecules whereas Ti-inserted TiC3H3 complex adsorbs less number of H2 molecules than that of Ti-capped TiC3H3 complex. Nature of interactions between different molecules in hydrogen-adsorbed complexes is studied. The binding energy per H2 molecules differ by about 0.1 eV in transition metal-capped and transition metal-inserted structures.

Singlet–triplet (S 0 → T 1) excitation energies of the [4 × n] rectangular graphene nanoribbon series ( n = 2–6): A comparative theoretical study

Singlet–triplet (S 0 → T 1) well-to-well (WWE S–T) and vertical (VE S–T) excitation energies of the [4 × n] rectangular graphene nanoribbon series ( n = 2–6) were estimated using various semiempirical, Hartree–Fock (HF), density functional (DFT), and second order Moller–Plesset perturbation theory methods with the assumption of a closed-shell singlet state. Significant model chemistry dependent variability in theoretically obtained WWE S–T/VE S–T is evident for the rectangular graphene nanoribbons. With the exception of the B2PLYP density functional (which, along with the mPW2PLYP functional, combines exact HF exchange with an MP2-like correlation to the DFT calculation), all DFT, semiempirical, and HF methods investigated predict the onset of a negative WWE S–T/VE S–T (ground state triplet) starting somewhere between the [4 × 3] through [4 × 6] derivatives, with most functionals predicting a transition from a singlet to triplet ground state between the [4 × 4] and [4 × 5] rectangular graphene nanoribbons. Consistent with previous work on the n-acene series, MP2 WWE S–T/VE S–T estimates have a significant positive systematic bias and HF estimates have substantial negative systematic biases. Extrapolation of the B2PLYP results, which are in excellent agreement with prior FPA-QZ VE S–T estimates, for any [ m × n] rectangular graphene nanoribbon derivatives predicts a vanishingly small singlet–triplet gap at the polymeric limit ( m → ∞ and/or n → ∞).

Theoretical calculations of molecular dipole moment, polarizability, and first hyperpolarizability of glycine–sodium nitrate

In order to calculate the energy gap, molecular dipole moment, polarizability, and first hyperpolarizability of glycine–sodium nitrate (Na(NO 3)·C 2H 5NO 2), a series of basis sets including polarized and diffuse functions have been employed at the framework of: Hartree–Fock, Density Functional Theory, and Möller–Plesset Perturbation Theory methods. Geometry optimization was carried out with DFT-B3LYP 6-311++G(d,p). The geometrical differences between the optimized molecule and the molecule in solid phase were attributed to intramolecular and intermolecular forces that are present in solid phase. In addition, the results have revealed that hydrogen bonds not only play an important role determining the crystal structure of glycine–sodium nitrate but also decreasing its energy gap. Further, it was confirmed that glycine–sodium nitrate has absolute value of dipole moment which is mainly caused by both the glycine dipolar character and the molecular geometry. Likewise, the calculations gave non-zero values of polarizability and first hyperpolarizability which are related to the linear and nonlinear responses, respectively.

The influence of M…M attraction on nonlinear optical properties of (XMPH3)2 (X = F, Cl; and M = Au, Ag and Cu): A theoretical study

AbstractIt is well known that the aurophilic attraction has great influence on spectra properties. There are certain relationships between spectra and nonlinear optical properties (NLO). Here, XMPH3, (XMPH3)2 (X = F, Cl; M = Au, Ag, and Cu) were taken as the examples to be investigated to study the relationship between NLO and M···M interactions. The NLO properties of XMPH3, (XMPH3)2 (X = F, Cl; M = Au, Ag, and Cu) were carried out with finite field/second‐order Møller–Plesset perturbation theory method. The results show that polarizability tensors of dimers (αtot,d) and second‐order hyperpolarizability tensors of dimers (γtot,d) are significantly larger than αtot,m and γtot,m of corresponding monomers. It indicates that M…M interaction significantly increases αtot,d and γtot,d values. The analysis of the electronic transition shows that the charge transfer along M…M direction play the key role on increasing αtot,d and γtot,d. On the other hand, the βtot is significantly increased by changing ligands and is slightly influenced by M…M interaction. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Dative stabilization of carbocations

Carbocations are well known intermediates in organic chemistry. While many carbocations are not stable enough to exist themselves, they may be stabilized by several factors, including resonance with nearby electron donors. Reactions that proceed via mechanisms involving carbocations include the Baeyer–Villiger reaction and the Criegee rearrangement. In both cases, the carbocation is stabilized through resonance by an oxygen atom. The role that oxygen plays in stabilizing carbocations was studied theoretically. The structures of several carbocations, based on the t-butyl ion, with varying numbers of oxygen atoms were optimized using second order Møller–Plesset perturbation theory methods. Relationships were found between the number of oxygen atoms and the amount of delocalization, as well as the charge of the formally positive carbon atom and the number of oxygen atoms bonded to it. Another study was performed on a set of larger cations. Evidence was found relating to the presence of dative bonds, the strength of which were found to be dependent on a number of factors.

POST HARTREE–FOCK AND DENSITY FUNCTIONAL THEORY STUDIES ON (BN)n=1–10 CLUSTERS

Density functional theory and Møller–Plesset perturbation theory methods have been used to study the ring clusters of ( BN )n=1–10 employing 6-311++G** basis set. The binding energies have been corrected for the basis set superposition error (BSSE). Static polarizability of these ring clusters has been investigated. A simple expression for the size dependence of polarizability has been invoked, so that the same relation can be useful for predicting the polarizability of larger clusters. The topological properties were analyzed employing the Bader's atoms in molecules theory. A good correlation between the structural parameters and the properties of electron density is found. Localization and delocalization indices were also used for the analysis of molecular electronic structure by an electron pair perspective. The contribution of stereo electronic interactions to the molecular properties as a function of ring size is analyzed based on the natural bond orbital (NBO) analysis.

The interaction of fluorosilanes with hydrogen fluoride clusters: strongly blue-shifted hydrogen bonds

The equilibrium structures, binding energies, and vibrational spectra of the complexes formed between hydrogen fluoride clusters (HF) n (1≤ n≤4) and the fluorosilanes SiHF 3, SiH 2F 2, and SiH 3F are investigated within the second-order Møller–Plesset perturbation theory method applying extended basis sets. It is shown that Si–F⋯H–F halogen–hydrogen bonds are formed in the most stable open dimers, SiHF 3–HF, SiH 2F 2⋯HF, and SiH 3F⋯HF. No Si–H⋯F–H hydrogen bonds occur in these dimers. Nevertheless, blue shifts of Si–H stretching frequencies are calculated. All three trimers, fluorosilane–(HF) 2, all three tetramers, fluorosilane–(HF) 3, and two of the pentamers, fluorosilane–(HF) 4, form cyclic structures with strong Si–F⋯H–F halogen–hydrogen bonds and weak Si–H⋯F–H contacts, the latter displaying, nevertheless, strongly blue-shifted Si–H stretching frequencies. These blue shifts are comparable in size to those of the corresponding fluoromethane–(HF) n complexes and are with about +50 cm −1 for the case n=3 among the largest ever calculated and definitely the largest for Si–H bonds. In the title complexes, the formation of the Si–F⋯H–F halogen–hydrogen bonds induces a substantial stretching of this Si–F bond, which in turn leads to a significant contraction of the fluorosilane Si–H bond in the Si–H⋯F–H hydrogen bond. This disposition of the fluorosilane monomers is demonstrated with the aid of suitable potential energy surface scans and appears to be a prerequisite for the formation of strongly blue-shifted hydrogen bonds.

Calculated Infrared, Raman, and Rayleigh Properties of the CO3 Molecule

Properties associated with the infrared, Rayleigh, and Raman spectra of the CO3 molecule are calculated by the Hartree–Fock and Møller–Plesset perturbation theory methods. Vibrational frequencies and infrared activities are found to be in agreement with the experiment and previous calculations. The values obtained for the Raman spectrum show a very sensitive dependence to the treatment of electron correlation. The OCO wag normal mode, unobserved in the IR experiment, is predicted to have a very small Raman scattering activity.

Predicting the binding energies of H-bonded complexes: A comparative DFT study

Comparisons with the results of coupled cluster calculations were made to assess the quality of density functionals in predicting the electronic binding energies of H-bonded complexes. A variety of different density functionals, namely B3LYP, B97-1, PBE0, HCTH, BLYP, PBE, LDA and a recently derived improvement of the HCTH functional (HCTH38), as well as the standard abinitio Hartree–Fock and second-order Moller–Plesset perturbation theory methods were applied using a triple-ζ plus double polarisation basis set. Equilibrium structures, counterpoise corrected binding energies and harmonic frequencies were calculated for the (HF)2, (HCl)2, (H2O)2, (CO)(HF), (OC)(HF), (FH)(NH3), (ClH)(NH3), (H2O)(NH3) and (H3O+)(H2O) complexes. Although the hybrid methods performed well in general, the new HCTH38 functional as a pure GGA predicted binding energies of better quality than the B3LYP functional. Bond length changes and frequency shifts were compared to MP2 results.