SCM's periodic density functional theory program, BAND, has undergone significant efficiency increases since its release in the fall of last year. Computer programmers and users know that disk speed is slower than RAM speed and as such programs that limit access to disk can function more quickly as a result. Two ways of doing this are by limiting the size of stored data sets by not including any unnecessary degree of precision, and by simply re-computing data sets that can be discarded and re-created faster than they can be written and read. The latest upgrades to the BAND program employ both of these time saving techniques. The improvement can be seen in the example jobs below:
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The crystalline system on the left is YBa2Cu3O7.
For a sample job the time to complete one SCF cycle dropped from approximately 1 hour and 50 minutes to only 15 minutes
when run on a desktop computer running the Windows 7 operating system with a quad-core 2.67GHz Intel Xenon processor and 4GB of RAM.
In the slower calculation the load on the processor cores repeatedly drops while the program waits for disk access,
whereas in the faster calculation with the new default parameters for the development version of BAND, all 4 cores of the processor remain at full load during this part of the calculation.
The same results are produced in each calculation.
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Note that these changes are currently available in the development snapshots of our programs, which can be downloaded at http://www.scm.com/SCMForms/DownloadSnapshots.jsp.
The Augmented Roothaan-Hall Direct Inversion Iterative Subspace (ADIIS) scheme by Xiangqian Hu and Weitao Yang, J. Chem Phys 132, 054109 (2010) has now been implemented in ADF. According to preliminary tests, this algorithm performs much better than Energy-DIIS. Additionally, unlike EDIIS, ADIIS does not require calculation of the total energy, so it is much faster. The ADIIS scheme in ADF has also been extended to support relativistic Spin-Orbit SCF calculations.
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The cobalt-centered molecule to the left is the central region of the B-12 vitamin. With the new ADIIS option enabled the SCF for this molecule converges in 52 steps at the LDA/TZP level. Without ADIIS no convergence could be obtained due to the small HOMO-LUMO gap (~10meV) of the system. |
This feature is now available in the development snapshots of ADF, versions r23063 and later, as well as in the Fix2009 snapshots, version r23064 and later. They can be downloaded at http://www.scm.com/SCMForms/DownloadSnapshots.jsp and http://www.scm.com/SCMForms/DownloadSnapshots.jsp?branch=fix2009, respectively. The text for the usage of ADIIS can be found in the developer's change-log at: http://www.scm.com/Downloads/ChangeLog-trunk.html.
Stefan Grimme's latest dispersion correction is now available in the development snapshots of ADF and BAND. Grimme and his coworkers at the Universität Münster outlined the parameterization of this new correction, dubbed DFT-D3, in a recent issue of The Journal of Chemical Physics 132, 154104 (2010). Here they list the advantages of the new method as the following:
Above: The adsorption energy of perylene-tetracarboxylic-dianhydride (PTCDA) on a gold (111) surface as a function of distance. Results without (PBE) and with dispersion corrections (PBE-D2, PBE-D3) are shown. The experimental distance is 3.27Å. The vdW-DF result is from PCCP, 12, 4759 (2010).
The article continues by, among other things, demonstrating how this new DFT-D version decreases the mean absolute deviations for a benchmark set of non-covalent interactions by 15-40% over the previous version. Professor Grimme notes that the more significant errors in dispersion energy can be expected for modeling highly charged systems. See section III-F of the original paper for more details.
DFT-D3 is now available in the development snapshots of ADF and BAND, versions r23091 and later. They can be downloaded at http://www.scm.com/SCMForms/DownloadSnapshots.jsp. Instructions on the use of this functional can be found in the ADF developer's change-log at http://www.scm.com/Downloads/ChangeLog-trunk.html.
SCM now has a YouTube channel. Here we will be uploading videos demonstrating the capabilities of our software as well as walk-through instructions on how to use it. Right now there are two demonstration videos online, as well as seven others which are walkthrough of the BAND and COSMO-RS GUI tutorials.
The videos are recorded at the 720p HDTV (1280x720) resolution, which should be clearly viewable on most computer monitors particularly if the full screen is used. The demo videos contains some instrumental background music, while the tutorial videos contain voice-over commentary and optional subtitles. All of our videos can be found on our video page at http://www.scm.com/Videos/Welcome.html Videos for the ADF-GUI tutorials will be uploaded here as soon as they are complete.
We will continue our regular participation in the ACS meetings when we attend the Fall 2010 ACS meeting in Boston, Massachusetts. Look for us there at booth 939 this August 22-25. We will conclude this year's tour of the USA in lucky booth number 113 at the Pacifichem 2010 conference in Honolulu, Hawaii. Those of you fortunate enough to be in the Aloha State this December 15-20 are more than welcome to stop by and talk with us about the latest innovations in ADF, BAND, COSMO-RS and our new Reax-FF program.
We always welcome suggestions for new ADF functionality that you would like to see included in a future release. Any questions or comments regarding this Newsletter, or other questions related to ADF, are also welcome and can be sent to info@scm.com. Feel free to contact us also in case you have some information that may be of interest to other ADF users, and that may be suitable material for a future Newsletter or news item on the SCM website.
These news items and more can be found in the news section of our website.
