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WIREs Comput Mol Sci
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Recent developments in the PQS program

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An overview of the PQS quantum chemistry suite is presented, with emphasis on recent developments and features that are unique to the program. The capabilities of the program, in particular the parallel implementation, are briefly described. Topics discussed in more detail are coupled‐cluster and other high‐level correlation methods, second‐order Møller–Plesset perturbation theory for large molecules, the Fourier transform Coulomb method, geometry optimization, in particular constrained and enforced geometry optimization, and properties such as vibrational circular dichroism, scaled quantum mechanical force fields, spin densities, and spatially modulated polarizabilities. © 2011 John Wiley & Sons, Ltd.

Figure 1.

Parallel scaling of QCISD(T) calculations on aspirin (6‐311G** basis, 282 basis functions, 34 correlated orbitals) and sucrose (6‐31G** basis, 455 basis functions, 68 correlated orbitals). The QCISD and (T) scaling, relative to a four‐processor calculation, are plotted separately. The cluster used dual‐core 3‐GHz Intel Pentium D930 processors (see comments in Figure 2) with one process running per node. (Timings are about 20% worse if both cores are running). Note the slightly superlinear speedup for the larger (T) calculation. The absolute timings on 16 processors are 3.8 and 53.7 min, respectively, for the QCISD calculations; for the perturbative (T) triples, they are 53.7 min and 50.5 h, respectively. Absolute timings are reduced by about a factor of two on the latest generation of processors.

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Figure 2.

Parallel scaling of a moderate‐sized MP2 calculation (6‐311G** basis, 990 basis functions) on alanine octapeptide with a number of processing cores. The scaling is plotted relative to a two‐processor calculation. Older Intel Pentium® D930 3‐GHz dual‐core CPUs were used; see Figure 1. The absolute time on 25 cores is 25.1 min.

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Figure 3.

Predicted metastable C2v ‘fused sandwich’ isomer of C12H10N2, obtained by applying an external force between six pairs of carbon atoms, one from each of the two benzene rings, in cis‐azobenzene.

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Figure 4.

The highest energy molecular orbital (HOMO, in transparent mode) and simulated vibrational circular dichroism (VCD) spectrum of 5‐helicene, calculated on a Windows 7 laptop computer.

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