MOLECULES IN OPTICAL, ELECTRIC, AND MAGNETIC FIELDS: A Personal Perspective

Abstract

Physical chemistry and theoretical chemistry have advanced over the past 50 years from being largely qualitative to having a mature status based firmly on the principles of quantum and statistical mechanics. My interest in the chemical elements and their compounds has prompted me to learn more about the nature of matter through the measurement and interpretation of optical, electric, and magnetic properties of molecules. In addition to holding intrinsic interest, such properties tell us about charge and current distributions and form the basis of electro-optics, magneto-optics, and nonlinear optics. They also help us understand the nature and strength of long-range intermolecular forces, the hydrogen bond, and molecular biology-topics that are apparently forever young. STUDENT DAYSWhen I was an undergraduate in the Faculty of Science at the University of Sydney in Australia, in 1948, there was an emphasis on bulk properties, thermodynamics, aqueous solutions, electrochemistry, and chemical kinetics. Quantum theory was for physicists rather than chemists, who were expected to have only sufficient acquaintance with quantum mechanics to enable them to read books such as Pauling's The Nature of the Chemical Bond (1). Yet chemistry is essentially a quantum phenomenon, and quantum mechanics had reached maturity 20 years earlier. , and me). I had a love from boyhood for the elements and their physical and chemical properties, so I decided to concentrate on chemistry. My older brother, Michael, favored physics, and I learned through him the importance of mathematics and fundamentals. MJ Buckingham made significant contributions to low-tempterature physics and to the theory of critical phenomena (6, 7). He was Professor of Theoretical Physics at the University of Western Australia from 1965 to 1992. An honours degree in science at Sydney takes four years and permits the study of several subjects. I took mathematics, physics, and chemistry for two years, and in my third year I took mathematics and chemistry while the organic chemists took chemistry and organic chemistry.In my fourth undergraduate year I joined the research group of RJW Le Fèvre, who was Professor of Chemistry at the University of Sydney from 1946 to 1970. He had an international reputation for his studies of physical properties of organic molecules (8-11). His most significant contribution to research was the experimental exploration and utilization, in cooperation with his wife, of a simple tensor-additivity model of anisotropic bond polarizabilities (Figure 1) (10). Atomic, bond, or group isotropic polarizabilities had previously been shown to be approximately additive, thereby providing a method for estimating the mean polarizability of a molecule (12). But the tensor addition of anisotropic bond polarizabilities provided a more demanding test of the assumption of additivity. Silberstein (13) had shown as early as 1917 that for two interacting spheres, classical dipolar interaction leads to an induced anisotropy in the polarizability, which var...

Frequency-Dependent Molecular Polarizability Calculated within an Interaction Model

“…Furthermore, as discussed recently, the limit for increasing the density of transistors in traditional silicon-based electronic devices will soon be reached . Therefore, an understanding at the molecular level of not only static (hyper)polarizabilities but also their frequency-dependent counterparts is of fundamental importance. − Quantum chemical methods can be used to calculate molecular frequency-dependent (hyper)polarizabilities but currently, accurate calculations are limited to rather small molecules due to the large requirement of computer resources. Extensions of computational methods to large molecules, and for example molecular crystals as well as effects from the surrounding medium are therefore limitted to less sophisticated models.…”

Relativistic four-component calculations of Buckingham birefringence using London atomic orbitals

“…The discrepancies between theory and experiment for these quantities are also responsible for our underestimation of the magnitude of m Q(x, T) for CO 2 and CS 2 , the HF values being closer to experiment than the DFT values. A reasonable value for the static electric field gradient in measurements of Buckingham birefringence is rE & 1 9 10 9 Vm -2 .…”

“…In this communication, we study relativistic effects on the Buckingham birefringence for the series of molecules CX 2 (X = O, S, Se, Te). For CO 2 , CS 2 and CSe 2 , we compare our results with previous nonrelativistic ab initio [17] data and with experiment [29][30][31][32][33][34]. The atomic-orbital-driven (AO-driven) scheme recently introduced by Bast et al [35] for calculating time-dependent molecular properties with one-, two-and four-component relativistic methods is extended to first-order frequency-dependent magnetic perturbations with London atomic orbitals (LAOs) [36][37][38][39][40], thereby ensuring gaugeorigin independence of the calculated results.…”

Role of quantum chemical calculations in molecular biophysics with a historical perspective

“…With the experimental Synchrotron Radiation Circular Dichroism (SRCD) technique now available for making measurments even farther in the UV range, clearly the tools of TD-DFT and wave function basd quantum mechancs have a lot of offer in the understanding and interpretiton of the exciting new experimental results [243]. In addition, some non linear optical methods have been proposed [244] and a general perspective paper on molecules in both electric and magnetic fields has appeared [245]. The effects of the solvent on vibrational frequencies have also recently been investigated and a new partitioning of the contributions causing the solvent effects has been proposed [246].…”