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Articles 1 - 16 of 16
Full-Text Articles in Physical Sciences and Mathematics
Electronic Structure And Bonding In Metal Porphyrins, Metal=Fe, Co, Ni, Cu, Zn, M.-S. Liao, Steve Scheiner
Electronic Structure And Bonding In Metal Porphyrins, Metal=Fe, Co, Ni, Cu, Zn, M.-S. Liao, Steve Scheiner
Steve Scheiner
A systematic theoretical study of the electronic structure and bonding in metal meso-tetraphenyl porphines MTPP, M=Fe, Co, Ni, Cu, Zn has been carried out using a density functional theory method. The calculations provide a clear elucidation of the ground states for the MTPPs and for a series of [MTPP]x ions (x = 2+, 1+, 1−, 2−, 3−, 4−), which aids in understanding a number of observed electronic properties. The calculation supports the experimental assignment of unligated FeTPP as 3A2g, which arises from the configuration (dxy)2(dz …
Electronic Structure And Bonding In Unligated And Ligated Feii Porphyrins, M.-S. Liao, Steve Scheiner
Electronic Structure And Bonding In Unligated And Ligated Feii Porphyrins, M.-S. Liao, Steve Scheiner
Steve Scheiner
The electronic structure and bonding in a series of unligated and ligated FeII porphyrins (FeP) are investigated by density functional theory (DFT). All the unligated four-coordinate iron porphyrins have a 3A2g ground state that arises from the (dxy)2(dz2)2(dπ)2 configuration. The calculations confirm experimental results on Fe tetraphenylporphine but do not support the resonance Raman assignment of Fe octaethylporphine as 3Eg, nor the early assignment of Fe octamethyltetrabenzporphine as 5B2g. For the six-coordinate Fe–P( …
Comparison Of Methods For Calculating The Properties Of Intramolecular Hydrogen Bonds. Excited State Proton Transfer, T. Kar, Steve Scheiner, M. Cuma
Comparison Of Methods For Calculating The Properties Of Intramolecular Hydrogen Bonds. Excited State Proton Transfer, T. Kar, Steve Scheiner, M. Cuma
Steve Scheiner
A series of molecules related to malonaldehyde, containing an intramolecular H-bond, are used as the testbed for a variety of levels of ab initio calculation. Of particular interest are the excitation energies of the first set of valence excited states, nπ∗ and ππ∗, both singlet and triplet, as well as the energetics of proton transfer in each state. Taking coupled cluster results as a point of reference, configuration interaction-singles–second-order Møller–Plesset (CIS–MP2) excitation energies are too large, as are CIS to a lesser extent, although these approaches successfully reproduce the order of the various states. The …
Characterization Of Ground And Excited Electronic State Deprotonation Energies Of Systems Containing Double Bonds Using Natural Bond Orbital Analysis, J. K. Badenhoop, Steve Scheiner
Characterization Of Ground And Excited Electronic State Deprotonation Energies Of Systems Containing Double Bonds Using Natural Bond Orbital Analysis, J. K. Badenhoop, Steve Scheiner
Steve Scheiner
Natural bond orbital analysis is applied to the ground and excited states of a set of neutral, cationic, and anionic doubly bonded species HnC=XHn (X=C, N, O) isoelectronic with ethylene. The character of the excitation is correlated with calculated charge shifts and geometry changes upon relaxation. For these planar molecules, depopulation of the π bond or population of the π∗ antibond causes an out‐of‐plane twist or pyramidalization upon relaxation correlated to the amount of charge shift. These nonplanar distortions generally lower the energy more than changes in bond lengths and angles. Population of a σXH∗ …
Proton‐Donor Properties Of Water And Ammonia In Van Der Waals Complexes. Be–H2o And Be–Nh3, G. Chalasinski, M. M. Szczesniak, Steve Scheiner
Proton‐Donor Properties Of Water And Ammonia In Van Der Waals Complexes. Be–H2o And Be–Nh3, G. Chalasinski, M. M. Szczesniak, Steve Scheiner
Steve Scheiner
The potential energy surfaces (PES) of Be–H2O and Be–NH3 are studied with particular attention to characterization of proton‐donor properties of water and ammonia. Calculations were performed by means of both supermolecular and intermolecular Møller Plesset perturbation theory. The Be–H2O PES reveals two van der Waals minima: the C2v minimum (De=176 cm−1, Re=6.5 bohr), and the H‐bonded minimum (De=161 cm−1, Re=7.5 bohr), separated by a barrier of 43 cm−1 at the T‐shaped configuration. The Be–NH3 PES reveals only …
Calculation Of Barriers To Proton Transfer Using Variations Of Multi-Configuration Self‐Consistent Field Methods. I. Combinations Of Orbitals, K. Luth, Steve Scheiner
Calculation Of Barriers To Proton Transfer Using Variations Of Multi-Configuration Self‐Consistent Field Methods. I. Combinations Of Orbitals, K. Luth, Steve Scheiner
Steve Scheiner
The usefulness of multiconfiguration self‐consistent‐field (MCSCF) calculations in computing correlated proton transfer potentials is investigated for the systems HF2−, H7N2+, H3O2−, and H5O2+. In deciding whether to include particular molecular orbitals, it is important to consider the balance of electron density between the donor and acceptor groups and the interactions that are incorporated in the orbitals. Only orbitals which have the proper symmetry to interact with the transferring hydrogen need be included in the MCSCF active space. Reasonable transfer barriers are obtained …
Proton–Donor Properties Of Water And Ammonia In Van Der Waals Complexes With Rare‐Gas Atoms. Kr–H2o And Kr–Nh3, G. Chalasinski, M. M. Szczesniak, Steve Scheiner
Proton–Donor Properties Of Water And Ammonia In Van Der Waals Complexes With Rare‐Gas Atoms. Kr–H2o And Kr–Nh3, G. Chalasinski, M. M. Szczesniak, Steve Scheiner
Steve Scheiner
The perturbation theory of intermolecular forces in conjunction with the supermolecular Møller–Plesset perturbation theory is applied to the analysis of the potential‐energy surfaces of Kr–H2O and Kr–NH3 complexes. The valleylike minimum region on the potential‐energy surface of Kr–H2O ranges from the coplanar geometry with the C2 axis of H2O nearly perpendicular to the O–Kr axis (T structure) to the H‐bond structure in which Kr faces the H atom of H2O. Compared to the previously studied Ar–H2O [J. Chem. Phys. 94, 2807 (1991)] the minimum has more …
Ab Initio Study Of The Intermolecular Potential Of Ar–H2o, G. Chalasinski, M. M. Szczesniak, Steve Scheiner
Ab Initio Study Of The Intermolecular Potential Of Ar–H2o, G. Chalasinski, M. M. Szczesniak, Steve Scheiner
Steve Scheiner
The combination of supermolecular Møller–Plesset treatment with the perturbation theory of intermolecular forces is applied in the analysis of the potential‐energy surface of Ar–H2O. The surface is very isotropic with the lowest barrier for rotation of ∼35 cm−1 above the absolute minimum. The lower bound for De is found to be 108 cm−1 and the complex reveals a very floppy structure, with Ar moving freely from the H‐bridged structure to the coplanar and almost perpendicular arrangement of the C2 –water axis and the Ar–O axis, ‘‘T‐shaped’’ structure. This motion is almost isoenergetic (energy change …
Ab Initio Study Of Intermolecular Potential Of H2o Trimer, G. Chalasinski, M. M. Szczesniak, P. Cieplak, Steve Scheiner
Ab Initio Study Of Intermolecular Potential Of H2o Trimer, G. Chalasinski, M. M. Szczesniak, P. Cieplak, Steve Scheiner
Steve Scheiner
Nonadditive contribution to the interaction energy in water trimer is analyzed in terms of Heitler–London exchange, SCF deformation, induction and dispersion nonadditivities. Nonadditivity originates mainly from the SCF deformation effect which is due to electric polarization. However, polarization does not serve as a universal mechanism for nonadditivity in water. In the double‐donor configuration, for example, the Heitler–London exchange contribution is the most important and polarization yields the wrong sign. Correlation effects do not contribute significantly to the nonadditivity. A detailed analysis of the pair potential is also provided. The present two‐body potential and its components are compared to the existing …
Theoretical Vibrational Study Of Fx...Nh3 (X=H, D, Li) Complexes, Y. Bouteiller, Z. Latajka, H. Ratajczak, Steve Scheiner
Theoretical Vibrational Study Of Fx...Nh3 (X=H, D, Li) Complexes, Y. Bouteiller, Z. Latajka, H. Ratajczak, Steve Scheiner
Steve Scheiner
This paper presents the first ab initio attempt to construct the stretching fundamentals νFX and νF...N (X=H, D, Li) in the FX...NH3 complexes taking into account the mechanical anharmonicity. A potential‐energy surface V(rFX,RF...N) grid was generated at the self‐consistent‐field and second‐order Møller–Plesset levels. The coefficients fitting the potential‐energy surface up to the fourth order have been used to compute the νFX and νF...N stretching modes. The vibrational problem is solved by means of a variational treatment which includes the effects of mechanical …
Effect Of Intermolecular Orientation Upon Proton Transfer Within A Polarizable Medium, Steve Scheiner, X. Duan
Effect Of Intermolecular Orientation Upon Proton Transfer Within A Polarizable Medium, Steve Scheiner, X. Duan
Steve Scheiner
Ab initio calculations are used to investigate the proton transfer process in bacteriorhodopsin. HN = CH2 serves as a small prototype of the Schiff base while HCOO- models its carboxylate-containing counterion and HO- the hydroxyl group of water of tyrosine, leading to the HCOO-.H+.NHCH2 and HO-.H+.NHCH2 complexes. In isolation, both complexes prefer a neutral pair configuration wherein the central proton is associated with the anion. However, the Schiff base may be protonated in the former complex, producing the HCOO-.+HNHCH2 ion pair, when …
Nonadditive Effects In Hf And Hcl Trimers, G. Chalasinski, S. M. Cybulski, M. M. Szczesniak, Steve Scheiner
Nonadditive Effects In Hf And Hcl Trimers, G. Chalasinski, S. M. Cybulski, M. M. Szczesniak, Steve Scheiner
Steve Scheiner
Nonadditive effects are calculated for (HF)3 and (HCl)3 complexes and analyzed via the combination of perturbation theory of intermolecular forces with Møller–Plesset perturbation theory (MPPT). In both systems the nonadditivity is dominated by the self‐consistent field (SCF) deformation effect, i.e., mutual polarization of the monomer wavefunctions. Heitler–London exchange and correlation effects are of secondary importance. Three‐body terms exhibit much lesser basis set dependence than the two‐body effects and even quite moderate basis sets which are not accurate enough for treatment of two‐body forces can yield three‐body effects of quantitative quality. This is due in large measure to the …
Analysis Of The Potential Energy Surface Of Ar–Nh3, G. Chalasinski, S. M. Cybulski, M. M. Szczesniak, Steve Scheiner
Analysis Of The Potential Energy Surface Of Ar–Nh3, G. Chalasinski, S. M. Cybulski, M. M. Szczesniak, Steve Scheiner
Steve Scheiner
The combination of supermolecular Møller–Plesset treatment with the perturbation theory of intermolecular forces is applied in the analysis of the potential energy surface of Ar–NH3. Anisotropy of the self‐consistent field (SCF) potential is determined by the first‐order exchange repulsion. Second‐order dispersion energy, the dominating attractive contribution, is anisotropic in the reciprocal sense to the first‐order exchange, i.e., minima in one nearly coincide with maxima in the other. The estimated second‐order correlation correction to the exchange effect is nearly as large as a half ΔESCF in the minimum and has a ‘‘smoothing’’ effect on the anisotropy of …
Vibrational Frequencies And Intensities Of H‐Bonded And Li‐Bonded Complexes. H3n⋅⋅Hcl And H3n⋅⋅Licl, M. M. Szczesniak, I. J. Kurnig, Steve Scheiner
Vibrational Frequencies And Intensities Of H‐Bonded And Li‐Bonded Complexes. H3n⋅⋅Hcl And H3n⋅⋅Licl, M. M. Szczesniak, I. J. Kurnig, Steve Scheiner
Steve Scheiner
The geometries, energetics, and vibrational spectra are calculated for the two complexes at the SCF and correlated MP2 levels using the 6‐31G∗∗ basis set, augmented by a second set of d functions on Cl. While correlation represents an important factor in the binding of H3 N⋅⋅HCl, it contributes little to the stronger Li bond. Unlike the HCl stretch νs which decreases substantially in frequency and is greatly intensified in H3 N⋅⋅HCl, the frequency of the LiCl stretch undergoes an increase and little change is noted in its intensity, conforming to prior spectral measurements. The intensities of the …
Primary And Secondary Basis Set Superposition Error At The Scf And Mp2 Levels. H3n‐‐Li+ And H2o‐‐Li+, Zdzisław Latajka, Steve Scheiner
Primary And Secondary Basis Set Superposition Error At The Scf And Mp2 Levels. H3n‐‐Li+ And H2o‐‐Li+, Zdzisław Latajka, Steve Scheiner
Steve Scheiner
The primary basis set superposition error (BSSE) results from the artificial lowering of the energy of each subunit of a pair by the presence of ‘‘ghost orbitals’’ of its partner. In addition, these ghost orbitals perturb the one‐electron properties of the molecule, causing a change in the interaction energy, an effect known as secondary BSSE which is not corrected by the counterpoise procedure. The primary and secondary BSSE are calculated for the interactions of NH3 and H2O with Li+, using a variety of different basis sets. It is found that the 2° BSSE can be …
Vibrational Frequencies And Intensities Of H-Bonded Systems. 1:1 And 1:2 Complexes Of Nh3 And Ph3 With Hf, I. J. Kurnig, M. M. Szczesniak, Steve Scheiner
Vibrational Frequencies And Intensities Of H-Bonded Systems. 1:1 And 1:2 Complexes Of Nh3 And Ph3 With Hf, I. J. Kurnig, M. M. Szczesniak, Steve Scheiner
Steve Scheiner
Frequencies and intensities are calculated by ab initio methods for all vibrational modes of the 1:1 H3X–HF and 1:2 H3X–HF–HF complexes (X=N,P). The HF stretching frequencies are subject to red shifts, roughly proportional to the strength of the H bond, and to manyfold increases in intensity. Although the intramolecular frequency shifts within the proton acceptors are relatively modest, the intensities of the NH3 stretches are magnified by several orders of magnitude as a result of H bonding (in contrast to PH3 which exhibits little sensitivity in this regard). …