Reviews in Computational Chemistry Volume 18
Reviews in Computational Chemistry Volume 18
Reviews in Computational Chemistry Volume 18
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and<br />
Hss ¼ U rep<br />
ss<br />
1<br />
2<br />
X<br />
j;k<br />
ðmj þ p jÞ ~T jk ðm k þ p kÞþ 1<br />
2a<br />
X<br />
j<br />
½o 2<br />
e _p 2 j þ p2 j<br />
Š ½88Š<br />
Here, Tjk is the dipole–dipole <strong>in</strong>teraction tensor, and ~T jk ¼ Tjkð1 djkÞ; U rep<br />
0s<br />
and Urep ss stand for repulsion potentials, and o0 ¼ E12=h, where E12 is the<br />
adiabatic gas-phase energy gap (Eq. [29]).<br />
The statistical average over the electronic degrees of freedom <strong>in</strong> Eq. [15]<br />
is equivalent, <strong>in</strong> the Drude model, to <strong>in</strong>tegration over the <strong>in</strong>duced dipole<br />
moments p0 and pj. The Hamiltonian Hi is quadratic <strong>in</strong> the <strong>in</strong>duced dipoles,<br />
and the trace can be calculated exactly as a functional <strong>in</strong>tegral over the<br />
fluctuat<strong>in</strong>g fields p0 and pj. 39,67 The result<strong>in</strong>g solute–solvent <strong>in</strong>teraction energy<br />
is 67<br />
E0s;i ¼ Ii þ U rep<br />
0s<br />
þ Udisp<br />
0s;i aefeim 2 0i feim0i Rp<br />
1<br />
2 a0ifeiR 2 p<br />
Here, Rp is the reaction field of the solvent nuclear subsystem, and the factor<br />
fei ¼ ½12aea0iŠ 1<br />
describes an enhancement of the condensed-phase solute dipole and polarizability<br />
by the self-consistent field of the electronic polarization of the solvent.<br />
For the statistical average over the nuclear configurations, generat<strong>in</strong>g the<br />
distribution over the solute energy gaps (Eq. [<strong>18</strong>]), one needs to specify the<br />
fluctuation statistics of the nuclear reaction field Rp. A Gaussian statistics of<br />
the field fluctuations 35 implies us<strong>in</strong>g the distribution function<br />
½89Š<br />
½90Š<br />
PðRpÞ ¼ 4p apkBT 1=2 exp½ b R 2 p =4apŠ ½91Š<br />
where ap is the response coefficient of the nuclear solvent response. Comb<strong>in</strong>ed<br />
with the Gaussian function PðRpÞ, Eq. [89] is essentially equivalent to the Q<br />
model (Eq. [65]). The vector of the nuclear reaction field plays the role of the<br />
nuclear collective mode driv<strong>in</strong>g activated transitions (q). One can then directly<br />
employ the results of the Q model to produce the diabatic free energy surfaces<br />
of polarizable donor–acceptor complexes or to calculate the spectroscopic<br />
observables.<br />
The reorganization energies follow from Eq. [71] and take the follow<strong>in</strong>g<br />
form for polarizable chromophores:<br />
li ¼ðapfi=feiÞ ~m0 þ 2apfi ~a0m0i<br />
Beyond the Parabolas 177<br />
2<br />
½92Š