In quantum chemistry, the Dyall Hamiltonian is a modified Hamiltonian with two-electron nature. It can be written as follows:[1]
\hat{H}\rm=
\rmD | |
\hat{H} | |
i |
+
\rmD | |
\hat{H} | |
v |
+C
\rmD | |
\hat{H} | |
i |
=
\rmcore | |
\sum | |
i |
\varepsiloniEii+
\rmvirt | |
\sum | |
r |
\varepsilonrErr
\rmD | |
\hat{H} | |
v |
=
\rmact | |
\sum | |
ab |
\rmeff | |
h | |
ab |
Eab+
1 | |
2 |
\rmact | |
\sum | |
abcd |
\left\langleab\left.\right|cd\right\rangle\left(EacEbd-\deltabcEad\right)
C=2
\rmcore | |
\sum | |
i |
hii+
\rmcore | |
\sum | |
ij |
\left(2\left\langleij\left.\right|ij\right\rangle-\left\langleij\left.\right|ji\right\rangle\right)-2
\rmcore | |
\sum | |
i |
\varepsiloni
\rmeff | |
h | |
ab |
=hab+\sumj\left(2\left\langleaj\left.\right|bj\right\rangle- \left\langleaj\left.\right|jb\right\rangle\right)
where labels
i,j,\ldots
a,b,\ldots
r,s,\ldots
\varepsiloni
\varepsilonr
Emn
\dagger | |
a | |
m\alpha |
an\alpha+
\dagger | |
a | |
m\beta |
an\beta
S2
Sz
The Dyall Hamiltonian behaves like the true Hamiltonian inside the CAS space, having the same eigenvalues and eigenvectors of the true Hamiltonian projected onto the CAS space.