A beta version of the DL_LEED code was released in early 2000 and is currently undergoing testing. The full release version will be documented in the special CCP3 Issue of Computer Physics Communications and interfaced to the DL Visualize software for a final release in the autumn of 2000.
For further details see the article in Annex 5:
The Daresbury Laboratory Low Energy Electron Diffraction Package: DL_LEED
The development of the angle resolved photoemission code, PHOTON2, is aimed at providing a more efficient and robust calculation for a wider variety of surfaces. The code builds on the earlier generation of photoemission codes, PEOVER1 and NEWPOOL, to deal with surfaces with an arbitrary number of atoms per layer unit cell and with arbitrary numbers of overlayers and layers in the bulk repeat unit. No-scattering and multiple-scattering, direct and Kambe summation options enable efficient calculation of the hole state for shallow and deep levels. A number of scattering approximations including, single scattering, re-normalised forward scattering and multiple scattering have been implemented to accelerate the calculation of the final state.
Work has progressed on validating and testing the code on Beryllium and Copper test cases. Technical problems were found in using the variable phase equations to generate accurate regular and irregular solutions to the variable phase equations for negative core energies, energies near to the muffin-tin zero and high energies typically used in photoelectron diffraction calculations. The variable phase solver is being reimplemented with a different choice of baseline solutions. Work is well underway to document the code which will be published in the special CCP3 Issue of Computer Physics Communications in the autumn of 2000.
The first principles (density functional theory and Hartree-Fock) package CRYSTAL is the subject of the current CCP3 grant. The development of fast analytic gradients will allow the study of complex surface structures and chemical processes at surfaces. In addition a significant effort is being made to increase the ease of use of CRYSTAL, in particular: the maintenance and extension of the Cerius2 graphical user interface, the generation of better documentation and tutorial materials and the development of a Gaussian basis set library. These resources are being made available via the CRYSTAL WWW pages.
The implementation of analytic gradients of the energy with respect to atomic co-ordinates – forces is a key requirement for studies of large and complex geometries and has been the subject of the current CCP3 flagship proposal. A variety of algorithms for the simultaneous optimisation of internal co-ordinates and the unit cell have been implemented. Currently numerical gradients are used but exploitation of analytic gradients is planned in the near future.
Further details of this development can be found in the articles in Annex 5:
Analytical Hartree-Fock Gradients for Periodic Systems
Developments of the CRYSTAL Software.
During the last year the CCP3 working group decided that a number of older packages would be given 'unsupported' status in the program library. During the current year new packages will be added:
In addition to the codes listed above the following codes have been made available to the CCP3 community:
PAD: Analysis of photoelectron and Auger electron diffraction via the use of full multiple scattering cluster calculations. Codes developed by Prof. D Saldin at the University of Milwaukee, Wisconsin.
Holographic Inversion: Codes for the analysis of photoelectron and x-ray diffraction data via holographic inversion. Codes developed by M Van Hove, Berkeley, California.
FEFF: Multiple scattering calculations of XAFS and XANES spectra, Codes developed by J Rehr, University of Washington.