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In this paper, we present a new approach to treat the electronic structure of a molecule in solution. Unlike the hybrid-type method, such as the reference interaction site model self-consistent-field theory, the new approach describes not only the electronic structure of solute but also solute–solvent interactions in terms of the quantum chemistry based on the Hartree–Fock frozen density formulation. In the treatment, the quantum effect due to solvent, including exchange repulsion, is projected on to the solute Hamiltonian using the spectral representation method. The solvent distribution around the solute is handled by the integral equation theory of liquids. As illustrative applications of the approach, the electronic and solvation structure of noble atoms, neon and argon, in liquid neon are studied. We also investigate the electronic structure of an excess electron in liquid helium. The preliminary results demonstrate that the quantum-mechanical effect on the electronic and solvation structure of the solute due to solvent molecules is successfully represented by the new method.In this paper, we present a new approach to treat the electronic structure of a molecule in solution. Unlike the hybrid-type method, such as the reference interaction site model self-consistent-field theory, the new approach describes not only the electronic structure of solute but also solute–solvent interactions in terms of the quantum chemistry based on the Hartree–Fock frozen density formulation. In the treatment, the quantum effect due to solvent, including exchange repulsion, is projected on to the solute Hamiltonian using the spectral representation method. The solvent distribution around the solute is handled by the integral equation theory of liquids. As illustrative applications of the approach, the electronic and solvation structure of noble atoms, neon and argon, in liquid neon are studied. We also investigate the electronic structure of an excess electron in liquid helium. The preliminary results demonstrate that the quantum-mechanical effect on the electronic and solvation structure of the s...

Quasirelativistic theory of magnetic shielding constants based on the Douglas–Kroll–Hess transformation of the magnetic potential presented in a previous paper is extended to molecular systems that contain heavy elements. The gauge-including atomic orbital method is adapted to the quasirelativistic Hamiltonian to allow origin-independent calculations. The present theory is applied to the proton and halogen magnetic shielding constants of hydrogen halides and the 199Hg magnetic shielding constants and chemical shifts of mercury dihalides and methyl mercury halides. While the relativistic correction to the magnetic interaction term has little effect on the proton magnetic shielding constants, this correction is a dominant origin of the heavy atom shifts of the magnetic shielding constants of heavy halogens and mercury. The basis set-dependence of mercury shielding constants is quite large in the relativistic calculation; it is important to use the basis functions that are optimized by the relativistic metho...

The fifth-order two-dimensional (2D) Raman signals have been calculated from the equilibrium and nonequilibrium (finite field) molecular dynamics simulations. The equilibrium method evaluates response functions with equilibrium trajectories, while the nonequilibrium method calculates a molecular polarizability from nonequilibrium trajectories for different pulse configurations and sequences. In this paper, we introduce an efficient algorithm which hybridizes the existing two methods to avoid the time-consuming calculations of the stability matrices which are inherent in the equilibrium method. Using nonequilibrium trajectories for a single laser excitation, we are able to dramatically simplify the sampling process. With this approach, the 2D Raman signals for liquid xenon, carbon disulfide, water, acetonitrile, and formamide are calculated and discussed. Intensities of 2D Raman signals are also estimated and the peak strength of formamide is found to be only five times smaller than that of carbon disulfide.

The reactivity and spectra of formaldehyde isomers and dimeric complexes between them are studied with ab initio methods. A large number of complexes between H2CO, trans-HCOH, cis-HCOH is calculated. Infrared and Raman spectra of (H2CO)2 are calculated with relatively simple methods using spectroscopic masses and scaled force constants. In this way, the structure of dimers in matrices can be deduced. Hydroxycarbene (HCOH) plays a key role in a model that explains a large number of experimental facts of the nonzero pressure photochemistry. Hydroxycarbene forms complexes with H2CO; the stabilization is due to classical hydrogen bonds. HCOH is a new example of an ambiphilic carbene. Addition products are formed from HCOH···H2CO complexes. The calculations show that, in agreement with matrix experiments, glycoaldehyde and methanol are easily formed. The formation of trans-HCOH occurs through a dimeric interaction with the shifting hydrogen. This bimolecular process is 9.6 kcal/mol (6–31G*) in favor of the unimolecular conversion. cis-HCOH might be formed via a nonplanar transition state, where also stabilization at the carbenic center is possible. When higher concentrations of HCOH are available, a hydrogen exchange mechanism easily transfers hydroxycarbene back to H2CO. Several experiments are suggested in this paper; notably, molecular beam and isotopic-mixture experiments will give useful information. The involvement of HCOH in the light-induced formose reaction is suggested.