Concise Physical Chemistry

c20 JWBS043-Rogers September 13, 2010 11:29 Printer Name: Yet to Come

STORED PARAMETERS 327

# sto-2g

hatom

02

h

FILE 20.3 (Input) An STO-2G input file using a stored basis set.

GFinputinserted after# sto-2gin theroute sectionof the input file produces

the added information. The parameterized STO-2G basis function is

STO-2G= 0. 4301 e−^1.^309 r

2

+ 0. 6789 e−^0.^233 r

2

which is not too far from the arbitrary function we guessed for input file,

File 20.1. The stored function is graphed in Fig. 20.5. The coefficients0.4301

and0.6789give the intercepts of the two Gaussians atr=0. As before, the two

αparameters determine how extended the Gaussian is in therdirection (how fat the

tail of the function is), and twoCparameters determine how much of a contribution

each Gaussian makes to the final STO approximation. Stored parameters have been

optimized for general application to molecular problems more complex than the hy-

drogen atom, which accounts for the “overshoot” ofα 1 = 1 .31 arrived at in the final

compromise.

STO-2G =C 1 e−α^1 r

2

+C 2 e−α^2 r

2

α 1 = 1. 31 ,α 2 = 0. 233

C 1 = 0. 430 , C 2 = 0. 679

We now have two ways of inserting parameters into the STO-2G calculation. We can

write them out in agenfile like input File 20.1 if we know the parameters we want,

or we can use the stored parameters as in input File 20.3 if we don’t. And we can use

theGFInputkeyword to find out what stored parameters were used. This process

can be carried further for the STO-3G, STO-4G, and many other atomic orbital

approximations. The stored parameters for some orbitals are quite cumbersome, and

one would not want to enter them by hand.

AO basis set in the form of general basis input:

10

S 2 1.00 0.000000000000

0.1309756377D+01 0.4301284983D+00

0.2331359749D+00 0.6789135305D+00

****

FILE 20.4 (Output) GAUSSIAN©Cstored parameters for the STO-2G basis set.