B. Montanari

Density functional study of molecular crystals: Polyethylene and a crystalline analog of bisphenol-A polycarbonate

Density functional calculations have been performed on two types of molecular crystal: (a) crystalline (orthorhombic) polyethylene comprising covalently bonded parallel chains with weak interchain interactions, and (b) a crystalline analog of bisphenol-A polycarbonate with a unit cell containing two molecules with 59 atoms each. The local density approximation for the exchange-correlation energy overestimates the strength of the intermolecular bonds in both, and the Becke–Perdew functional (gradient corrected) gives no intermolecular binding in the former and a very weak bond in the latter. The functional of Perdew, Burke, and Ernzerhof leads to binding in both molecules.

Density functional study of crystalline polyethylene

Abstract Density functional calculations have been performed for single chains and the crystalline (orthorhombic) form of polyethylene (PE). The geometrical structures are optimized without constraints, and the exchange-correlation energy is calculated using local density (LD) and non-local (gradient-corrected, GC) approximations. Both give good descriptions of the structure of a single PE chain, but LD calculations overestimate the binding energies between chains, and GC calculations lead to no interchain binding at all.

Density functional study of carbonic acid clusters

Density functional calculations on carbonic acid H2CO3 are extended to clusters of up to five such units. The most stable forms are the linear, hydrogen-bonded analogs of the dimer with anti–anti orientation. We calculate structures and vibration frequencies, as well as the energy required to bend and stretch the linear isomers. Linear chains of up to ∼20 units should be favored over ring structures, and they have a tensile strength reminiscent of chains of water molecules. We also discuss planar, nonlinear structures as well as three-dimensional isomers.

Density functional study of polypropylene and its submolecules

Previous density functional (DF) calculations of the structures of small hydrocarbon molecules (CH, CH2, C2H2, C2H4, C3H6, C3H8) have been extended to larger systems. The structure of a single chain of isotactic polypropylene (it-PP) has been optimized, and calculations have been performed for smaller molecules with closely related structures (propane C3H8, several conformers of isopentane C5H12, and 2,4,6-trimethyl heptane C10H22) using both local spin density (LSD) and non-local (gradient-corrected) energy functionals. The pronounced transferability of the local structural parameters between C5H12, C10H22 and it-PP suggests that the energy surfaces calculated for molecules with five carbon atoms should provide a very good representation of the local energy variations in much larger systems.

InAs/GaSb(001) valence-band offset: Independence of interface composition and strain

The InAs/GaSb(001) valence‐band offset is calculated for the two inequivalent GaAs‐like and InSb‐like interfaces and found to coincide to within ≊30 meV. This result is rationalized and generalized to arbitrary composition profiles and induced strain by using a simple model, based on the linear response theory, which is validated by a number of accurate first‐principles calculations for intermixed interfaces.