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In this work, two exercises are described that are designed to teach students about the evolution and behavior of the electronic bands of graphene and bilayer graphene. These exercises involve performing extended Hückel molecular orbital theory calculations on polyacenes and polycyclic aromatic hydrocarbons. In the first exercise, students investigate how the molecular orbitals of polyacenes converge into bands as polyacene size increases. Further, students learn that long-range interactions cause frontier-orbital crossing as the size of the polyacene increases. In the second exercise, the concepts of band structures, band crossing, and k-space are explored using the results of frontier orbital calculations on [pi]-stacked dimers of polycyclic aromatic hydrocarbons, which represent molecular analogues of layered 2D materials. The results of these calculations show how the geometry and layer-layer offset of the dimer system can affect its electronic structure, and the results can be extrapolated to provide a framework for understanding why subtle changes in the relative orientations of the layers in bilayer graphene can produce qualitative changes in the electronic properties. These calculations are easily implemented with Python or with widely available algebraic manipulation software such as Maple or Mathematica. These exercises are accessible to students who have experience with extended Hückel molecular orbital theory and are suitable for inclusion in the physical chemistry curriculum at the upper-level undergraduate or introductory graduate level.

Switchable rotaxanes are good candidates for molecular machines because of their ability to undergo reversible and repeatable co-conformational isomerism in response to an external stimulus. An acid-base switchable [2](2)rotaxane reported by Li et al. [J Org Chem. 79(15): [6996–7004] has been reported to exhibit a 48% change in length upon a stimulus-induced change in protonation state, suggesting that it could serve as the fundamental element of a 'molecular muscle'. In the present work, the mechanical behaviour of this topologically complex system is explored with calculations based on semiempirical electronic structure theory. Our calculations predict that the original system will not work as envisioned. Although the calculations confirm a 48% change in length, they also reveal an energy barrier to ring shuttling upon deprotonation, preventing the immediate delivery of force. Therefore, a modification to the system is proposed. Similar semiempirical calculations were carried out on the modified system and the force calculated. The average force generated from the modified system is predicted to be approximately −86 pN. The results demonstrate that the proposed modification reduces the force generated by ring shuttling by 11% but largely eliminates the energy barrier to ring shuttling so that the force is immediately available. [ABSTRACT FROM AUTHOR]

Herein, a slightly enhanced version of extended Huckel molecular orbital theory is applied to demonstrate the spontaneous distortion of 1,3,5,7-cyclooctatetraene from a perfect octagon, a consequence of the Jahn-Teller effect. The exercise is accessible to students who have been introduced to basic quantum mechanics and extended Huckel molecular orbital theory and is easily implemented with widely available algebraic manipulation software such as Maple or Mathematica. This exercise is suitable for inclusion in the physical chemistry curriculum at the upper-level undergraduate or introductory graduate level. (Contains 7 figures.)

Five different physically motivated analytic isotherm models are fit to experimental (P , V) data from seven different sources reporting studies of the adsorption of CO2 by activated carbon. The model behavior upon parameter optimization suggests that multi-layer adsorption does not play a dominant role in CO2 uptake by activated carbon. Only by explicitly modeling two distinct types of binding sites in the first adsorption layer does the model fully capture the nuances of the data. The values of the best-fit parameters provide good support for a widely used structural model of activated carbon: that it may be represented by nanoscopic flakes of hexagonally bonded carbon, the edges of which are terminated by functional groups. This conclusion is confirmed by comparison of the fitting parameter values to published results of first-principles calculations of the interaction of CO2 with systems having chemical features representative of this structural model. [ABSTRACT FROM AUTHOR]

The vibrational analysis with a lumped-inertia technique can efficiently and reliably anticipated certain vibrational properties without the need for performing costly comprehensive full normal-mode computations is demonstrated. The model affords a portioning of the effect of phenyl ring substituents on the torsional vibrational frequencies between inertial and electronic structure contributions.

Research into the surface structures of gamma- and eta-alumina is presented.

The transition aluminas, gamma-alumina, eta-alumina and delta-alumina are known to have a spinel structure but the possibility that they contain hydrogen is not clear. A series of density functional theory computations which, together with available experimental data, demonstrate that the spinel aluminas exist over a range of hydrogen content, is presented. The spinel aluminas are shown to have the empirical formula H(sub 3m)Al(sub 2-m)O(sub 3), with various greek-letter phases corresponding to different distributions of the Al ions on two cation sublattices.