Q-Chem

UniChem (we tested Version 4.1) is a graphic interface made for running calculations on remote machines. The UniChem GUI runs on the local workstation and submits the computations to be run on a remote machine. The server software comes with MNDO, DGauss, and CADPAC. It can also be used as a graphic interface for Gaussian and Q-Chem. A toolkit can be purchased separately, which allows users to create an interface to their own programs. 

Q-Chem (we tested Version 1.2) is an ah intio program designed for efficient calculations on large molecules. Q-Chem uses ASCII input and output files. 

The HyperChem program from Hypercube Inc. and UniChem from Oxford Molecular can be used as graphic interfaces to Q-Chem. At the time we conducted our tests, it was not yet available on all the platforms listed as being supported. The current version is well designed for ground- and excited-state calculations on small or large organic molecules. 

Q-Chem includes HF, ROHF, UHF, and MP2 Hamiltonians as well as a good selection of DFT functionals. Mulliken and NBO population analysis methods are available. Multiple options are available for SCF convergence, geometry optimization, and initial guess. IR and Raman intensities can also be computed. In addition, the documentation was well written. 

One of the major selling points of Q-Chem is its use of a continuous fast multipole method (CFMM) for linear scaling DFT calculations. Our tests comparing Gaussian FMM and Q-Chem CFMM indicated some calculations where Gaussian used less CPU time by as much as 6% and other cases where Q-Chem ran faster by as much as 43%. Q-Chem also required more memory to run. Both direct and semidirect integral evaluation routines are available in Q-Chem. 

Gaussian users will find that Q-Chem feels familiar. The ASCII input format is a bit more wordy than Gaussian it is more similar to GAMESS input. The output is very similar to Gaussian output, but a bit cleaner. The code can easily be used with a job-queueing system. 

Q-Chem also has a number of methods for electronic excited-state calculations, such as CIS, RPA, XCIS, and CIS(D). It also includes attachment-detachment analysis of excited-state wave functions. The program was robust for both single point and geometry optimized excited-state calculations that we tried. 

Revh.ock. J.F., Hirlbirt, H.Z.. Brake, D.R.. Lang, E G., and Kern. D.Q. Chem. Eng. Prog. Symposium Series No. 30. 56 (1960) 161 Heat and mass transfer analogy An appraisal using plant scale data. 

Stewart, J. J. P. 1996. Applications of Localized Molecular-Orbitals to the Solution of Semiempirical Self-Consistent-Fielf Equations. Int. J. Q. Chem. 58,133. 

Glossman, M. D., L. C. Baibas, A. Rubio, and I. A. Alonso. 1994. Nonlocal Exchange and Kinetic Energy Density Functionals with Correct Asymptotic Behavior for Electronic Systems. Int. I. Q. Chem. 49, 171. 

Ooi, S., Carter, D., Fernando, Q. Progress in coordination chemistry, Proc. 11th Intemat. Conf. Coord. Chem., Haifa and Jerusalem 1968, (ed. M. Cais). New York Elsevier Pubh ing Co. 1968, D43 — Shiro, M., Fernando, Q. Chem. Commun. 1971, 350 see also Ref. 7 )... 

This book derives from materials and experience accumulated at Wavefunction and Q-Chem over the past several years. Philip Klunzinger and Jurgen Schnitker at Wavefunction and Martin Head-Gordon and Peter Gill at Q-Chem warrant special mention, but the book owes much to members of both companies, both past and present. Special thanks goes to Pamela Ohsan and Philip Keck for turning a sloppy manuscripf into a finished book. 

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