A formula to calculate the charge penetration energy that results when two charge densities overlap has been derived for molecules described by an effective fragment potential (EFP). The method has been compared with the ab initio charge penetration, taken to be the difference between the electrostatic energy from a Morokuma analysis and Stone's Distributed Multipole Analysis. The average absolute difference between the EFP method and the ab initio charge penetration for dimers of methanol, acetonitrile, acetone, DMSO, and dichloromethane at their respective equilibrium geometries is 0.32 kcal mol −1 . Walter J. Stevens Physical and Chemical Properties Division (838), National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8380 ͑Received 30 December 1999; accepted 10 February 2000͒ Keywords Ab initio calculations, Carrier density, Electrostatics Disciplines Chemistry Comments This article is fromA formula to calculate the charge penetration energy that results when two charge densities overlap has been derived for molecules described by an effective fragment potential ͑EFP͒. The method has been compared with the ab initio charge penetration, taken to be the difference between the electrostatic energy from a Morokuma analysis and Stone's Distributed Multipole Analysis. The average absolute difference between the EFP method and the ab initio charge penetration for dimers of methanol, acetonitrile, acetone, DMSO, and dichloromethane at their respective equilibrium geometries is 0.32 kcal mol Ϫ1 .

The effective fragment potential (EFP) method, is a discrete method for the treatment of solvent effects, originally formulated using Hartree-Fock (HF) theory. Here, a density functional theory(DFT) based implementation of the EFP method is presented for water as a solvent. In developing the DFT based EFP method for water, all molecular properties (multipole moments, polarizabilitytensors, screening parameters, and fitting parameters for the exchange repulsion potential) are recalculated and optimized, using the B3LYP functional. Initial tests for water dimer, small water clusters, and the glycine-water system show good agreement with ab initioand DFT calculations. Several computed properties exhibit marked improvement relative to the Hartree-Fock based method, presumably because the DFT based method includes some dynamic electron correlation through the corresponding functional. KeywordsDensity functional theory, Solvents, Ab initio calculations, Discrete systems, Electron correlation calculations Disciplines Chemistry CommentsThe following article appeared in Journal of Chemical Physics 118 (2003) The effective fragment potential ͑EFP͒ method, is a discrete method for the treatment of solvent effects, originally formulated using Hartree-Fock ͑HF͒ theory. Here, a density functional theory ͑DFT͒ based implementation of the EFP method is presented for water as a solvent. In developing the DFT based EFP method for water, all molecular properties ͑multipole moments, polarizability tensors, screening parameters, and fitting parameters for the exchange repulsion potential͒ are recalculated and optimized, using the B3LYP functional. Initial tests for water dimer, small water clusters, and the glycine-water system show good agreement with ab initio and DFT calculations. Several computed properties exhibit marked improvement relative to the Hartree-Fock based method, presumably because the DFT based method includes some dynamic electron correlation through the corresponding functional.

Prior to the first reported synthesis of the titanium analogue of ferrocene, bis(η5-cyclopentadienyl)Ti, there was theoretical speculation as to the electronic structure of what would become known as “titanocene”. In time, the original report of a successful synthesis was apparently shown to be incorrect, and a dimeric form of the substance was postulated as the correct structure. In the present work, high level ab initio and DFT calculations are performed on the titanocene monomer to help answer these structural questions, and to compare with early theoretical and experimental efforts. The need for a multi-configurational wave function is analyzed and found to be unnecessary. The present calculations predict that the ground state of titanocene monomer is a triplet with parallel and freely rotating cyclopentadienyl rings, which further suggests that experimentally synthesized “titanocene” is indeed some form of the dimer.

We formed the gas-phase β-ionone–O2 complex in a supersonic expansion and then photodissociated the complex with light near 312 nm. Photodissociation resulted in the production of O2 in the a 1Δg state, which was ionized at 312 nm using (2 + 1) resonance-enhanced multiphoton ionization (REMPI). We recorded the 1O2 REMPI action spectrum and O2 + velocity map ion image following photodissociation of the complex. From the velocity map image, we determined the total recoil kinetic energy distribution from dissociation of the complex. Fitting the REMPI spectrum showed that the 1O2 product has an effective rotational temperature of about 50 K, while the recoil kinetic energy distribution was well fit with a statistical Boltzmann distribution having an effective translational temperature of 289 K. Using the average translational energy from the Boltzmann fit along with the complex dissociation energy from ab initio calculations, we determined that β-ionone was formed with an average of 2.87 eV of internal energy, which was 0.49 eV higher than previous measurements for the β-ionone triplet-state energy. Our own CCSD/cc-pVDZ//(U)­MP2/cc-pVDZ calculations gave a minimum triplet-state energy of 2.04 eV. However, a large structural change occurs between the minimum singlet-ground-state geometry and the minimum triplet-excited-state geometry, and as a result, the calculated vertical energy for the triplet-state β-ionone was determined to be 3.30 eV. Comparing the ab initio and experimental results indicated that following excitation, β-ionone was formed in the triplet state but with significant internal vibrational energy. As such, complex dissociation likely proceeds following internal vibrational energy redistribution, which explains the statistical recoil kinetic energy distribution.

Requires Microsoft ExcelCourses in computational chemistry are increasingly common at the undergraduate level. Excellent user-friendly programs, which make the execution of ab initio calculations quite simple, are available. However, there is a danger that the underlying SCF procedure (usually coupled with contracted Gaussian atomic orbital basis sets) can become a 'black box' for the student. We have attempted to rectify this situation by creating a Microsoft Excel spreadsheet that contains all the essential elements of far more complicated ab initio calculations, but on the simplest possible molecular system. This submission performs Restricted Hartree-Fock (RHF) self-consistent field (SCF) calculations on a two-body, two-electron system. In addition, the spreadsheet makes use of standard minimal Gaussian basis sets for hydrogen and helium. Therefore, one can perform the following ab initio single-point energy calculations for H 2 , HeH + , or He 2 2+ :To fulfill the above pedagogical objectives, all the calculations are carried out using standard Excel cell formulas to make the entire procedure more transparent to the student. Specifically, the spreadsheet contains:• contracted Gaussian atomic orbital basis sets • calculation of one-and two-electron integrals• the construction of a Hamiltonian core initial molecular orbital (MO) guess, or the option for the student to provide their own initial MO guess This process is then repeated until self-consistency in the energy is achieved. The student is able to step through the SCF procedure one iteration at a time, or step through each part of one iteration; in the latter case, built-in macros walk the student through each step of the SCF cycle and highlight the relevant parts of the spreadsheet to show where a particular calculation is carried out.The spreadsheet makes use of these features:• The student can plot the highest occupied molecular orbital (ψ 1 ), lowest unoccupied molecular orbital (ψ 2 ), |ψ 1 | 2 , | ψ 2 | 2 , or any combination of the four during the SCF cycle. This allows the student to easily see how the wave function is being improved.• The contraction coefficients and Gaussian exponents can be changed to demonstrate the variational principle.• The electronic energy convergence threshold can be changed.The spreadsheet described here is accompanied by a manuscript that summarizes the RHF SCF method and presents the full form of all the working equations used in the spreadsheet.