in wave functions. It is the model which throws away absolutely everything
except the last bit, the only thing that if thrown away would leave nothing. So it
provides fundamental understanding” (R. Hoffmann, personal communication,
2002 February 13). SHM programs may be located by googling “simple huckel
method programs”. The program from the University of Calgary is recommended:
http://www.chem.ucalgary.ca/SHMO/This can be downloaded or used online.
SPARTANSpartan¼spare, uncomplicated. Marketed by Wavefunction
http://www.wavefun.com/
This is a suite of programs with MM (SYBYL and MMFF), ab initio, semiem-
pirical (MNDO, AM1, PM3) and DFT, with its own superb graphical user interface
(GUI) for building molecules, for calculations, and for viewing the resulting
geometries, vibrational frequencies, orbitals, electrostatic potential distributions,
etc. SPARTAN is a complete package in the sense that one does not need to buy
add-on programs like, say, a GUI. The programs is very easy to use and its algo-
rithms are robust – they usually accomplish their task, e.g. the sometimes tricky job
of finding a transition state usually works with SPARTAN. Versions of the program
are available for PCs running under Windows and LINUX, for Macs, and for UNIX
workstations. It lacks some high-level correlated ab initio methods, like CI, CC,
CASSCF, and its store of basis sets and DFT functionals is limited to the most
commonly used ones (the exact selection varies somewhat from version to version),
but it is nevertheless extremely useful for research, not to mention teaching.
9.3.2 Hardware.........................................................
Someone beginning computational chemistry might wish to get a high-end PC running
under Windows or LINUX: such a machine is fairly cheap and it will do even
sophisticated electron-correlation ab initio calculations. There is some prejudice in
the field against Windows, in favor of LINUX, but except for the highest-level
correlated calculations, it probably does not matter much which operating system
you use (some specialized programs are available only for LINUX). A ca. 3 GHz
quadcore machine with 4–8 GB of memory and a 1,000 GB hard drive is now (2010)
not unusual (soon it may be substandard). While this is a reasonable choice for
general computational chemistry, certain jobs may run faster on other configura-
tions of machine and operating system. Using standard Gaussian 94 test jobs
and various operating systems, and varying software and hardware parameters,
Nicklaus et al. comprehensively compared a wide range of “commodity computers”
[ 65 ]. These were ordinary personal computers of the time (ca. 1998); the costliest
was about US$5,000 and most were less than $3,000. A computer of this price
would now be roughly ten times as fast as in 1998. They concluded that “commod-
ity-type computers have...surpassed in power the more powerful workstations and
even supercomputers.... Their price/performance ratios will make them extremely
attractive for many chemists who do not have an unlimited budget...” Chemists
without unlimited budgets will be reassured to read a slightly more recent study, by
9.3 Software and Hardware 581