A general procedure is introduced for calculation of the electron correlation energy, starting from a single Hartree–Fock determinant. The normal equations of (linear) configuration interaction theory are modified by introducing new terms which are quadratic in the configuration coefficients and which ensure size consistency in the resulting total energy. When used in the truncated configuration space of single and double substitutions, the method, termed QCISD, leads to a tractable set of quadratic equations. The relation of this method to coupled‐cluster (CCSD) theory is discussed. A simplified method of adding corrections for triple substitutions is outlined, leading to a method termed QCISD(T). Both of these new procedures are tested (and compared with other procedures) by application to some small systems for which full configuration interaction results are available.

1.
(a)
C. A.
Bauschlicher
,Jr.
,
S. R.
Langhoff
,
P. R.
Taylor
, and
H.
Partridge
,
Chem. Phys. Lett.
126
,
436
(
1986
);
(b)
C. W.
Bauschlicher
,Jr.
,
S. R.
Langhoff
,
P. R.
Taylor
,
N. C.
Handy
, and
P. J.
Knowles
,
J. Chem. Phys.
85
,
1469
(
1986
);
(c)
C. W.
Bauschlicher
,Jr.
and
P. R.
Taylor
,
J. Chem. Phys.
85
,
2779
(
1986
); ,
J. Chem. Phys.
(d)
C. W.
Bauschlicher
, Jr.
and
P. R.
Taylor
,
85
,
6510
(
1986
).,
J. Chem. Phys.
2.
J. A.
Pople
,
J. S.
Binkley
, and
R.
Seeger
,
Int. J. Quantum Chem. Symp.
10
,
1
(
1976
).
3.
S. R.
Langhoff
and
E. R.
Davidson
,
Int. J. Quantum Chem.
8
,
61
(
1974
).
4.
R.
Krishnan
,
M. J.
Frisch
, and
J. A.
Pople
,
J. Chem. Phys.
72
,
4244
(
1980
).
5.
C.
Mo/ller
and
M. S.
Plesset
,
Phys. Rev.
46
,
618
(
1934
).
6.
(a)
P. J.
Knowles
,
K.
Somasundaram
,
N. C.
Handy
, and
K.
Hirao
,
Chem. Phys. Lett.
113
,
8
(
1985
);
(b)
W. D.
Laidig
,
G.
Fitzgerald
, and
R. J.
Bartlett
,
Chem. Phys. Lett.
113
,
151
(
1985
).,
Chem. Phys. Lett.
7.
J.
Cizek
,
J. Chem. Phys.
45
,
4256
(
1966
).
8.
R. J.
Bartlett
,
H.
Sekino
, and
G. D.
Purvis
, III
,
Chem. Phys. Lett.
98
,
66
(
1983
).
9.
S. J.
Cole
and
R. J.
Bartlett
,
J. Chem. Phys.
86
,
873
(
1987
).
10.
P. R.
Taylor
,
G. B.
Bacskay
,
N. S.
Huch
, and
A. C.
Hurley
,
Chem. Phys. Lett.
41
,
444
(
1976
).
11.
J. A.
Pople
,
R.
Krishnan
,
H. B.
Schlegel
, and
J. S.
Binkley
,
Int. J. Quantum Chem.
14
,
545
(
1978
).
12.
R. J.
Bartlett
and
G. D.
Purvis
, III
,
Int. J. Quantum Chem.
14
,
561
(
1978
).
13.
G. D.
Purvis
, III
and
R. J.
Bartlett
,
J. Chem. Phys.
76
,
1910
(
1982
).
14.
(a)
M.
Urban
,
J.
Noga
,
S. J.
Cole
, and
R. J.
Bartlett
,
J. Chem. Phys.
83
,
4041
(
1985
);
(b)
J.
Noga
and
R. J.
Bartlett
,
J. Chem. Phys.
86
,
7041
(
1987
).,
J. Chem. Phys.
15.
K.
Raghavachari
,
J. Chem. Phys.
82
,
4607
(
1985
).
16.
R. J. Bartlett has pointed out that the symbols C1,C2,⋯ are normally used for the substitution operators in CI wave functions, T1,T2,⋯ being reserved for the cluster operators of coupled cluster theory. In this paper, we use the symbols C1,C2,⋯ for substitution operators [defined by Eq. (2.2)] throughout, the difference between various correlation methods being accounted for by different values of the amplitudes aia,aijab,⋯
17.
W.
Meyer
,
Int. J. Quantum Chem.
5
,
341
(
1971
);
W.
Meyer
,
J. Chem. Phys.
58
,
1017
(
1973
).
18.
R.
Ahlrichs
,
P.
Scharf
, and
C.
Ehrhardt
,
J. Chem. Phys.
82
,
890
(
1985
).
19.
J. A.
Pople
,
R.
Seeger
, and
R.
Krishnan
,
Int. J. Quantum Chem. Symp.
11
,
149
(
1977
).
20.
R.
Krishnan
and
J. A.
Pople
,
Int. J. Quantum Chem.
14
,
91
(
1978
).
21.
Y. S.
Lee
and
R. J.
Bartlett
,
J. Chem. Phys.
80
,
4371
(
1984
).
This content is only available via PDF.
You do not currently have access to this content.