New features in Dalton 2.0

There are several new additions introduced in the Dalton 2.0. The most important and largest extension to the code is the addition of a complete Density Functional Theory (DFT) module, including up to quadratic response properties as well as an extensive open-shell (spin-restricted) module. The main new features and changes are summarized below:

1. Density Functional Theory:

   The largest new extension to Dalton 2.0 is the addition of a complete Density Functional Theory (DFT) module. It contains 24 different exchange-correlation functions, and is implemented for energies, linear and quadratic response functions (for both singlet and triplet perturbing operators) and geometric Hessians, nuclear shielding tensors, and magnizabilities as well as indirect spin-spin coupling constants. Energies and linear response properties are also available for spin-restricted, high-spin DFT (vide infra).

2. NEVPT2: Dalton 2.0 allows for the calculation of second-order MP2 energy corrections to an MCSCF reference wave function. The approach used here, the ``n-electron valence space second-order perturbation theory'' approach (NEVPT2) [5,6,7], is similar to CASPT2 [8], but is based on a two-electron zeroth-order Hamiltonian (the Dyall Hamiltonian [9]) and thus rarely displays problems with intruder states.

3. R12 methods: The R12 approach for obtaining basis-set limit MP2 energies are available in a couple of approximations [10,11].

4. Excited-state gradients: Excited-state gradients are available for singlet excited states for a Hartree-Fock reference wave function, calculated as the single residue of the quadratic response function. The excited-state gradients can be used to optimzie the structure of excited states using first-order optimization schemes.

5. Absorption in linear response: The linear reponse code now allows finite lifetimes for excited states [12], allowing both scattering and absorptions processes to be taken into account simultaneously.

6. Improvements for 64-bit machines: The code can now also calculate two-electron spin-orbit integrals as well as do AO2MO transformations for more than 255 basis functions also on 64-bit machines.

7. Extensions to the coupled cluster code: CCSD(T) energies and analytical gradients are now available.

8. Orbital exponent gradients: Gradients of the orbital exponents can now be calculated for closed-shell molecular species [].

9. Spin-spin coupling constants: Allows for the calculation of coupling constants to one single nucleus.

10. Changes to DALTON.INP: To harmonize the input for single-point and geometry optimization calculations, the labels for calculating molecular properties during a geometry optimization is changed such that

    Old label	New label
    **START	**START
    ****PROPERTIES	**EACH STEP
    ****FINAL	**PROPERTIES

11. New MOLECULE input format: There is now a new input structure for the MOLECULE input file. The new format is keyword driven and contains no fixed-format input lines unless the basis set is explicitely given in the input file. However, with the exception of the ATOMBASIS option, the input file is fully backward compatible with the old input format. For more information, see Sec. 23.

12. Single input file: In addition to the new input format for DALTON, DALTON now also allows the entire input to be given in a single file. This file must be started by the MOLECULE input on the first line, and the DALTON input is placed at the end of the input file. An optimization of methane may thus look like:

    BASIS
    aug-cc-pVDZ
    CH4  molecule. Basis: aug-cc-pVDZ.
    Geometry from JCP 112, 393 (2000).
    Atomtypes=2 Generators=2 Y X Angstrom
    Charge=6.0 Atoms=1
    C     0.000000       0.000000      0.000000
    Charge=1.0 Atoms=2
    H     0.889981273    0.000000000  -0.629311793
    H     0.000000000    0.889981273   0.629311793
    
    **DALTON INPUT
    .OPTIMIZE
    **WAVE FUNCTION
    .HF
    *END OF INPUT
    

    This single input file has to be named foo.dal, and only a single filename is given as arguments to the DALTON script, that is

    > ./dalton foo
    

13. More basis set directories: DALTON will now search for basis sets in any user specified directories, the job directory, and in the DALTON basis set library. DALTON 1.2 would search in only one directory, either a directory specified by the user or the DALTON basis set library.

14. Changes to basis set names: The following basis sets have been renamed from DALTON 1.2, largely for consistency with the EMSL basis set order form. Note that spaces are not permitted in basis set names.

    Old Label	New Label
    DunningDZ	DZ(Dunning)
    DunningTZ	TZ(Dunning)
    SVP(Dunning-Hay)+diffuse	SVP+Diffuse(Dunning-Hay)
    AhlrichsVDZ	Ahlrichs-VDZ
    AhlrichsVTZ	Ahlrichs-VTZ
    japrtano	Almlof-Taylor-ANO
    daug-cc-pVXZ (also t,q)	d-aug-cc-pVXZ (t-,q-)
    daug-cc-pCVXZ (also t,q)	d-aug-cc-pCVXZ (t-,q-)
    sadlej	Sadlej-pVTZ
    sad-J	Sadlej-pVTZ-J

15. Depricated features: PVM no longer supported: The parallel version no longer supports PVM as a message passing interface. Currently Dalton will only correctly install a parallel version using MPI. Note also that if a parallel DALTON is requested, the executable can both run parallel and sequential calculations.
16. Numerical Hessian in VROA/Raman calculations: The analytical Hessian is no longer required for the calculation of Raman intensities and Vibrational Raman optical activities. Instead, the Hessian may be calculated numerically using the analytical gradients. This can be achieved adding the keyword .NUMHES in the three input modules **START, **EACH S and **PROPER.