Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. The application of variational density functional perturbation theory ͑DFPT͒ to lattice dynamics and dielectric properties is discussed within the plane-wave pseudopotential formalism. We derive a method to calculate the linear response of the exchange-correlation potential in the GGA at arbitrary wavevector. We introduce an efficient self-consistent solver based on all-bands conjugate-gradient minimization of the second order energy, and compare the performance of preconditioning schemes. Lattice-dynamical and electronic structure consequences of space-group symmetry are described, particularly their use in reducing the computational effort required. We discuss the implementation in the CASTEP DFT modeling code, and how DFPT calculations may be efficiently performed on parallel computers. We present results on the lattice dynamics and dielectric properties of ␣-quartz, the hydrogen bonded crystal NaHF 2 and the liquid-crystal-forming molecule 5CB. Excellent agreement is found between theory and experiment within the GGA.

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. The structural and electronic properties of four L-amino acids alanine, leucine, isoleucine, and valine have been investigated using density functional theory ͑DFT͒ and the generalized gradient approximation. Within the crystals, it is found that the constituent molecules adopt zwitterionic configurations, in agreement with experimental work. Lattice constants are found to be in good agreement with experimentally determined values, although certain discrepancies do exist due to the description of van der Waals interactions. We find that these materials possess wide DFT band gaps in the region of 5 eV, with electrons highly localized to the constituent molecules. It is found that the main mechanisms behind crystal formation are dipolar interactions and hydrogen bonding of a primarily electrostatic character, in agreement with current biochemical understanding of these systems. The electronic structure suggests that the amine and carboxy functional groups are dominant in determining band structure.

We present an ab initio formalism for the calculation of transport properties in compositionally disordered systems within the framework of the Korringa-Kohn-Rostoker nonlocal coherent potential approximation. Our formalism is based on the single-particle Kubo-Greenwood linear response and provides a natural means of incorporating the effects of short-range order upon the transport properties. We demonstrate the efficacy of the formalism by examining the effects of short-range order and clustering upon the transport properties of disordered AgPd and CuZn alloys.

To investigate the merits of crystal structure prediction using ab initio computational techniques, we have used density functional (DFT) methods to investigate the relative stabilities of the four known crystalline phases of glycine and also a range of alternative putative crystal structures of the zwitterion. Energy differences are calculated using a range of exchange-correlation functionals, and it is found that the calculated relative stability of the phases is sensitive to the choice of functional. Energy differences are found to be on the order of a few tenths of a kilocalorie per mole with little separation in energy found between observed and putative structures. This result is similar to that typically obtained from force field calculations and confirms the difficulty of the task of predicting the structure of molecular crystals. Optimization of structures, including optimization of unit cells, highlights the limitation of DFT in describing the long-range dispersion interaction. Use of the local density approximation (LDA) is shown to over-bind crystals, whereas use of gradient-corrected functionals severely underbinds crystals. Calculated structural energy differences are presented, which show that, for the case of the LDA, the four observed glycine polymorphs receive a lower energy than all putative glycine structures considered.