Biomedical Engineering Reference
In-Depth Information
X
1
A
0
(or
X
1
A
Tabl e 6. 1
) ground state energies (in a.u.) and dipole
moments (in Debye), and the relative energies (in eV) of the lowest 15 excited states of
the nucleic acid bases
Adenine
The CASSCF
Guanine
Uracil
Cytosine
Thymine
464.6212766
539.476656
412.563491
392.691128
451.606027
4.61 (
3
A
0
)
3.93 (
3
A
0
)
3.87 (
3
A
0
)
3.53 (
3
A
0
)
3.86 (
3
A
)
5.47 (
3
A
0
)
5.02 (
3
A
0
)
4.75 (
3
A
00
)
4.63 (
3
A
0
)
4.85 (
3
A
)
5.87 (
3
A
0
)
5.53 (
3
A
00
)
4.92 (
1
A
00
)
4.64 (
3
A
00
)
5.03 (
1
A
)
6.13 (
1
A
0
)
5.66 (
1
A
00
)
5.49 (
3
A
0
)
4.75 (
1
A
0
)
5.54 (
3
A
)
6.39 (
3
A
0
)
5.75 (
3
A
0
)
6.29 (
3
A
00
)
4.75 (
1
A
00
)
6.36 (
3
A
)
7.09 (
1
A
0
)
6.07 (
1
A
0
)
6.36 (
3
A
0
)
5.35 (
3
A
00
)
6.38 (
3
A
)
7.34 (
3
A
00
)
6.58 (
1
A
0
)
6.49 (
1
A
00
)
5.39 (
3
A
0
)
6.56 (
1
A
)
7.41 (
1
A
00
)
6.85 (
3
A
00
)
6.59 (
1
A
0
)
5.55 (
3
A
00
)
6.62 (
1
A
)
7.82 (
1
A
0
)
7.11 (
1
A
00
)
7.00 (
1
A
0
)
5.57 (
1
A
00
)
7.20 (
1
A
)
7.85 (
3
A
00
)
7.14 (
3
A
0
)
7.70 (
3
A
0
)
5.64 (
1
A
00
)
7.78 (
3
A
)
8.09 (
1
A
00
)
7.84 (
3
A
00
)
7.78 (
3
A
00
)
6.48 (
1
A
0
)
7.92 (
3
A
)
9.38 (
3
A
00
)
7.98 (
1
A
00
)
7.89 (
1
A
00
)
6.92 (
3
A
0
)
7.98 (
1
A
)
9.43 (
1
A
00
)
8.12 (
3
A
00
)
7.93 (
3
A
00
)
7.93 (
3
A
0
)
7.98 (
3
A
)
11.21 (
3
A
00
)
8.14 (
1
A
00
)
7.96 (
1
A
00
)
7.98 (
3
A
00
)
8.05 (
1
A
)
11.23 (
1
A
00
)
8.14 (
1
A
0
)
8.56 (
3
A
0
)
7.98 (
1
A
00
)
8.71 (
1
A
)
3.96
a
3.06
1.58
4.06
6.33
a
Calculated ground state dipole moments.
Tabl e 6. 2
Configurations used in the CASSCF to generate the orbitals and in
the final CAS-CI model
Molecule
CAS
Configurations
Adenine
(12,10)
(1a'-29a')
58
,(30a',1a”-9a”)
12
(1a'-30a')
60
,(1a”-3a”)
6
,(31a',32a',4a”-10a”)
12
Guanine
(12,9)
Uracil
(14,10)
(1a' - 22a')
44
, (23a', 24a', 1a” - 8a”)
14
Cytosine
(14,10)
(1a' - 22a')
44
, (23a', 24a', 1a” - 8a”)
14
(1a - 26a)
52
, (27a- 36a)
14
Thymine
(14,10)
In the course of this work we have performed many scattering calculations and
this section will only summarise the results, see Table
6.3
. In doing this we have
chosen to select calculations performed in a uniform manner so that trends become
apparent, rather than taking calculations individually optimized for each system.
In particular we note that there are quite a number of ways of performing CC
calculations. Of particular significance is the choice as to whether to “contract” or
“uncontract” the configurations which involves placing the scattering electron in a
target virtual orbital [
43
].
Although the difference between these two approaches may seem technical they
actually differ quite significantly. The contracted method is standard but, without
