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WIREs Comput Mol Sci
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MOLCAS—a software for multiconfigurational quantum chemistry calculations

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At variance, with most of the quantum chemistry software presently available, MOLCAS is a package that is specialized in multiconfigurational wave function theory (MC‐WFT) rather than density functional theory (DFT). Given the much higher algorithmic complexity of MC‐WFT versus DFT, an extraordinary effort needs to be made from the programming point of view to achieve state‐of‐the‐art performance for large‐scale calculations. In particular, a robust and efficient implementation of the Cholesky decomposition techniques for handling two‐electron integrals has been developed which is unique to MOLCAS. Together with this ‘Cholesky infrastructure’, a powerful and multilayer graphical and scripting user interface is available, which is an essential ingredient for the setup of MC‐WFT calculations. These two aspects of the MOLCAS software constitute the focus of the present report. © 2012 John Wiley & Sons, Ltd.

Figure 1.

Example of polymetallic uranium oxide. At the level of density functional theory, this compound and its analogous nitride (central oxygen atom replaced by nitrogen) display the same equipartition of the spin density over the three uranium centers. CASPT2 reveals instead the true mixed valence nature unique to the oxide, a result that can be used in similar compounds for which X‐ray crystallographic data are inadequate to select the oxide/nitride alternative.

[ Normal View | Magnified View ]
Figure 2.

Flowchart of a sample geometry optimization (shown as Enhanced MOLCAS Input Language input on the top right). The different blocks correspond to the various modules of the MOLCAS program, each performing a specific task, as indicated in the associated box.

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Figure 3.

Example of visualization of molecular orbitals in graphical tool. The shown menu (available by right click of the mouse) exemplifies functionalities that allow for a fast selection/modification of the active space.

[ Normal View | Magnified View ]

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