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A particular goal of the COST action CODECS is to facilitate or enhance the interoperability of different quantum chemical programs to extend the range of spectroscopic applications that can be targeted.

Important aspects of this goal are:

Meta-Programs for Enhanced Functionality of Quantum Chemistry Codes

Several more specialized types of spectroscopic applications are not available as standard features in quantum chemistry software. Often, however, Quantum Chemistry groups have found smart solutions to work around such limitations.

As an example for vibrational spectroscopy, consider the calculation of the Hessian for a large molecular system. While most electronic-structure codes provide the possibility to do this without invoking external software, it may be advantageous to employ meta-programs such as SNF for improved parallelization or exploiting point-group symmetries not supported in your favorite electronic-structure code.

SNF also provides the possibility of a mode-wise calculation of intensities for vibrational spectra after an initial frequency analysis. In this way, the computational cost of Raman spectra calculations can considerably be reduced.

Also additional algorithmic features may be accessible through external programs, such as the optimization of selective Hessian eigenvectors (i.e., normal modes) within the so-called mode-tracking approach. This approach is implemented, e.g., in the program AKIRA, which is a meta-program that currently supports the electronic-structure codes DALTON, TURBOMOLE, ADF, and GAUSSIAN.

MoViPac unites the newest versions of both SNF and Akira alongside with a range of helpful add-ons to analyze and interpret the data obtained in the calculations. With its efficient parallelization scheme and meta-program design, it is particularly suited for the calculation of vibrational spectra of very large molecules.

Interfaces Connecting Several Quantum Chemistry Codes

One of the current efforts of COST-CODECS is to provide interface programs connecting several Quantum Chemistry packages. One example of such a tool is the PyADF scripting framework.

PyADF provides the possibility to define quantum-chemical workflows, in particular for multiscale simulations. Such applications generally require many individual quantum-chemical calculations, and the results of one calculation often serves as input subsequent ones. Moreover, different program packages might be necessary for different parts of the same workflow.

PyADF handles all steps of such workflows: In particular, it generates input files, runs the different program packages, extracts the results of these calculations and is able to transfer them between different programs. PyADF currently works with the software packages ADF, DALTON, and DIRAC.

Common Data Formats for Quantum Chemistry

Multiscale simulations using different quantum-chemical methods and program packages, such as those made possible by PyADF require the exchange of data between these different programs. This step would be greatly simplified by the definition of common data formats for quantum chemistry.

An important step towards a such a common Quantum Chemistry data format was achieved with Q5cost. It defines data formats based on XML and HDF5 for storing and exchanging information defining quantum-chemical calculations (e.g., geometry and basis set information) as well as for their results (e.g., molecular orbital coefficients). To facilitate multiscale simulations, work on using Q5cost within different quantum-chemical programs is in progress. To this end, tools are being developed for converting data in the programs' native format to Q5cost within PyADF.

Moreover, by annotating the programs' output file with XML tags it becomes possible to extract results of calculations easily. So far, this work has focused on the Dirac and Dalton program packages to establish best-practice guidelines for other codes.

Quantum Chemistry Modules/Codes

Gen1Int is a Fortran 90 library (with Python interface) to evaluate the derivatives of one-electron integrals with respect to the geometry perturbation, external electric and magnetic fields, and total rotational angular momentum at zero fields with contracted rotational London atomic orbitals (LAO). Relevant literature: B.Gao, A.J.Thorvaldsen, and K.Ruud: IJQC 2011 vol. 111 (4) pp. 858-872

XCFun is Arbitrary-Order Exchange-Correlation Functional Library. Relevant literature: U.Ekström, L.Visscher, R.Bast, A.J.Thorvaldsen, and K.Ruud, JCTC 2010 vol. 6 (7) pp. 1971-1980

The Gauge-Including Magnetically Induced Currents (GIMIC) program calculates, visualizes and analyzes magnetically induced currents in molecules. The GIMIC code implements the theory outlined in J.Juselius, D.Sundholm and J.Gauss, Calculation of Current Densities using Gauge-Including Atomic Orbitals, JCP 2004 vol. 121 (9) pp. 3952-3963. GIMIC is currently interfaced to CFOUR and Turbomole.

Data analysis or supporting tools

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