DALTON has the possibility of modelling the effect of a
surrounding linear, homogeneous dielectric
medium on a variety of molecular properties using
SCF or MCSCF
wave functions. This is achieved by the Multiconfigurational
Self-Consistent Reaction Field
(MCSCRF)
approach [93,94], where the solute is
placed in a spherical cavity and surrounded by the
dielectric medium. The solvent response to the presence of the
solute is modelled by a multipole
expansion, in DALTON in principle to infinite order, but
practical applications show that the multipole expansion is
usually converged at order 
.
In DALTON the solvent model is implemented both for SCF, DFT and MCSCF wave functions in a self-consistent manner as describes in Ref. [93,94]. In MCSCF calculations where MP2 orbitals is requested as starting orbitals for the MCSCF optimization, the solvent model will not be added before entering the MCSCF optimization stage, so MP2 gas-phase orbitals can be used as starting guess even though the solvent model has not been implemented for this wave function model. Note also that differential densities will be disabled in direct calculations when the solvent model is employed.
As regards molecular properties, the solvent model has so far been extended to singlet linear, quadratic and cubic response, and triplet linear response in the RESPONSE program, both using equilibrium and non-equilibrium solvation. A number of properties and excitation energies can be calculated with the (MC)SCRF model, and several studies of such properties have been presented, and we refer to these papers for an overview of what can currently be calculated with the approach [95,96], including ESR hyperfine coupling constants [97].
In addition, a non-equilibrium solvation model has been implemented for molecular energies [98]. This model in needed when studying processes where the charge distribution of the solute cannot be expected to be in equilibrium with the charge distribution of the solvent, e.g. when comparing with experiments where light has been used as a perturbation.
In the ABACUS program, the solvent model has been implemented for geometric distortions and nuclear shieldings and magnetizabilities, and of course all the properties that do not use perturbation-dependent basis sets, such as for instance indirect spin-spin coupling constants. This is noteworthy, as although the program will probably give results for most results calculated using the solvent model, these results will not necessarily be theoretically correct, due to lack of reorthonormalization contributions that have not been considered in the program. We therefore give a fairly complete literature reference of works that have been done with the program [99,100]. Properties not included in this list are thus not trustworthy with the current version of DALTON.