On Koopmans' theorem in density functional theory

This paper clarifies why long-range corrected (LC) density functional theory gives orbital energies quantitatively. First, the highest occupied molecular orbital and the lowest unoccupied molecular orbital energies of typical molecules are compared with the minus vertical ionization potentials (IPs) and electron affinities (EAs), respectively. Consequently, only LC exchange functionals are found to give the orbital energies close to the minus IPs and EAs, while other functionals considerably underestimate them. The reproducibility of orbital energies is hardly affected by the difference in the short-range part of LC functionals. Fractional occupation calculations are then carried out to clarify the reason for the accurate orbital energies of LC functionals. As a result, only LC functionals are found to keep the orbital energies almost constant for fractional occupied orbitals. The direct orbital energy dependence on the fractional occupation is expressed by the exchange self-interaction (SI) energy through the potential derivative of the exchange functional plus the Coulomb SI energy. On the basis of this, the exchange SI energies through the potential derivatives are compared with the minus Coulomb SI energy. Consequently, these are revealed to be cancelled out only by LC functionals except for H, He, and Ne atoms.     

An intramolecular nucleophilic substitution of oxetanes

The intramolecular attack of carbanions to oxetanes were examined and several three, five, and six membered carbocyclic compounds were synthesized.     

Photo-Reimer-Tiemann reaction of phenols,anilines and indolines

The photo-reaction of phenol (1) with chloroform in the presence of diethylamine gave salicylaldehyde (2) and 4-hydroxybenzaldehyde (3) in fair yield. Dihydroxybenzenes, sensitive to alkali, under similar conditions without the base gave corresponding aldehydes and a cyclohexa-2,5-dienone (15). The photo-reaction was also applied to diethylaniline (18), indoline (21) and N-methylindoline (24). In carbon tetrachloride instead of chloroform in an alcohol solution the same type of reaction took place to give esters. The mechanism involving the coupling of a phenoxy radical or a radical cation with dichloromethyl radical and not involving dichlorocarbene is proposed.     

Vibrational quasi-degenerate perturbation theory: applications to fermi resonance in CO2, H2CO, and C6H6

A quasi-degenerate perturbation method with vibrational self-consistent field (VSCF) reference wavefunction is developed. It simultaneously accounts for strong anharmonic mode-mode coupling among a few states (static correlation) by a configuration interaction theory and for weak coupling with a vast number of the other states (dynamic correlation) by a perturbation theory. A general formula is derived based on the van Vleck perturbation theory. An algorithm that selects a compact set of the most important VSCF configurations which contribute to the static correlation is proposed and a scheme to limit the number of configurations considered for dynamic correlation is also implemented. This method reproduces the vibrational frequencies of CO2 and H2CO that are subject to the strongest anharmonic mode-mode coupling within 10 cm(-1) of vibrational configuration interaction results in a computational expense reduced by a factor of one to two orders of magnitude. The method also reproduces the infrared absorption of C6H6 in the CH stretching (nu12) frequency region, in which combination tones nu13nu16 and nu2nu13nu18 appear on account of an intensity borrowing from nu12via the anharmonic coupling.     

Characterization of atmospheric tritiated water concentration in the vicinity of the fukushima daiichi nuclear power plant

Journal of Radioanalytical and Nuclear Chemistry - This paper discusses the spatiotemporal variation in atmospheric tritiated water (HTO) concentration near the Fukushima Daiichi Nuclear Power...     

Long-range corrected density functional calculations of chemical reactions: redetermination of parameter

Chemical reaction calculations were carried out using the long-range correction (LC) scheme, which improves long-range exchange effects in density functional theory (DFT) [J. Chem. Phys. 115, 3540 (2001); 120, 8425 (2004)]. A new determination of the LC scheme parameter mu was made by a root mean square fit of the percent error in calculated atomization energies. As a result, the parameter mu was optimized as 0.47, which is higher than the previous one (mu=0.33). Using this new parameter mu, LC-DFT was firstly applied to geometry optimizations of the G2 benchmark set molecules. Consequently, this new LC-DFT gave more accurate bond lengths and bond angles than previous LC-DFT and hybrid B3LYP results. Following this result, the authors calculated reaction barrier height energies of benchmark reaction sets, which have been underestimated in conventional DFT calculations. Calculated results showed that LC-DFT provided much more accurate barrier height energies with errors less than half those of previous LC-DFT and B3LYP studies. To test the general validity of the new LC-DFT, the authors finally calculated reaction enthalpies. As a result, they found that the LC scheme using the new mu clearly improved the accuracy of calculated enthalpies. The authors therefore conclude that the insufficient inclusion of long-range exchange effects is responsible for the underestimation of reaction barriers in DFT calculations and that LC-DFT using the new parameter is a powerful tool for theoretically investigating chemical reactions.     

Unnatural base pair systems toward the expansion of the genetic alphabet in the central dogma

Toward the expansion of the genetic alphabet of DNA, several artificial third base pairs (unnatural base pairs) have been created. Synthetic DNAs containing the unnatural base pairs can be amplified faithfully by PCR, along with the natural A-T and G-C pairs, and transcribed into RNA. The unnatural base pair systems now have high potential to open the door to next generation biotechnology. The creation of unnatural base pairs is a consequence of repeating "proof of concept" experiments. In the process, initially designed base pairs were modified to address their weak points. Some of them were artificially evolved to ones with higher efficiency and selectivity in polymerase reactions, while others were eliminated from the analysis. Here, we describe the process of unnatural base pair development, as well as the tests of their applications.(Communicated by Takao SEKIYA, M.J.A.).