The DALTON program system is designed to allow convenient,
automated determination of a large number of molecular properties
based on an HF, DFT, MP2, coupled cluster, or MCSCF reference wave
function. Additions to the Dalton 2.0 release include
density functional theory implemented fully up to quadratic response
theory for closed-shell systems, as well as second derivatives for
properties involving perturbation-dependent basis sets such a
molecular Hessians, magnetizabilities and nuclear shieldings. Also
available is the NEVPT2 approach
(the 
-electron valence second-order perturbation theory) for
calculating accurate energetics of
multireference-based systems including also dynamic electron
correlation, and highly accurate MP2-R12
methods are available for high-accuracy energetics of
single-reference dominated closed-shell systems.
The program consists of seven separate components, developed more or less independently. HERMIT is the integral generator, generating ordinary atomic and molecular integrals appearing in the time-independent, non-relativistic Schrödinger equation, as well as an extensive number of integrals related to different molecular properties. ERI is a vectorized and distribution-oriented integral generator that may be invoked in certain calculations, in particular in integral-direct coupled cluster calculations. SIRIUS is the (MC)SCF wave function optimization part, and is described comprehensively in the METECC-94 book [1]. ABACUS evaluates the second-order molecular properties of interest for SCF and MCSCF wave functions as well density-functional theory, in particular second-order static molecular properties in which the basis set depends on the applied perturbation. RESPONSE is a general-purpose program for evaluating response functions, up to cubic response functions for (MC)SCF wave functions, quadratic response for DFT, and linear response for the Second-Order Polarization Propagator Approximation (SOPPA) and Second-Order Polarization Propagator Approximation with Coupled Cluster Singles and Doubles Amplitudes - SOPPA(CCSD). A new density functional theory module has been added in the 2.0 release of the program. Existing modules have been extended with the NEVPT2 and the MP2-R12 methodologies.
Throughout this manual there will be references to articles describing the implementation of a specific molecular property or input option. This will hopefully suffice to give the reader a proper theoretical understanding of the current implementation. Only one reference otherwise not mentioned in the text, the treatment of symmetry, is given here [2].
DALTON is in many respects an ``expert's'' program. This is most noticeable in the range and selection of molecular properties that may be calculated and the flexibility and stability of the wave function implementations available. As described in the individual sections, the range of molecular properties, some of which are highly non-standard, is fairly large. On the other hand, several common properties can perhaps more easily be calculated using other, (non-)commercially available, quantum chemistry program packages.
We have tried when writing this manual to emphasize the modularity of the input, as well as indicating the advantages that may be obtained from the flexibility of the input. Yet, whether the authors of this manual have succeeded or not, is up to the reader to decide, and any comments and suggestions for improvements, both on the manual as well as the program, will be much welcome.