Wave function input examples

Those who are used to the old SIRIUS input will not experience any dramatic changes with respect to the DALTON input, although a few minor differences exist in order to create a more user-friendly environment. The input sections are the same as before starting with a wavefunction specification, currently, including options for SCF, DFT, MP2, MCSCF, and CC reference states. Depending on this choice of reference state the following input sections take different form, from the simplest SCF input to the more complex MCSCF input. Minimal SCF and SCF+MP2 using the new feature of generating the HF occupation on the basis of an initial Hückel calculation and then possibly change the occupation during the first DIIS iterations will be shown. There will also be an example showing how an old SIRIUS.RST file is used for restart in the input. In this case the Hartree-Fock occupation will be read from the file SIRIUS.RST and used as initial Hartree-Fock occupation. The HF occupation is needed for an MCSCF calculation, as this is anyway determined when establishing a suitably chosen active space. An example of an MCSCF-CAS input without starting orbitals will be given, as well as an MCSCF-RAS with starting orbitals. We note that an MCSCF wave function by default will be optimized using spin-adapted configurations (CSFs). The three following examples illustrate calculations on and excited state, on a core-hole state with frozen core orbital and on a core-hole state with relaxed core orbital. The last example shows an MCSCF calculation of non-equilibrium solvation energy. For examples on how to run CC wave functions, we refer to Chapter 20.

The following input example gives a minimal SCF input with default starting orbitals (that is, Hückel guess), and automatic Hartree-Fock occupation, first based on the Hückel guess, and then updated during the DIIS iterations:

**DALTON INPUT
.RUN WAVE FUNCTIONS
**WAVE FUNCTIONS
.HF
**END OF DALTON INPUT

The following input give a minimal input for an MP2 calculation using all default settings for the Hartree-Fock calculation (see previous example):

**DALTON INPUT
.RUN WAVE FUNCTIONS
**WAVE FUNCTIONS
.HF
.MP2
**END OF DALTON INPUT

If we would like to calculate molecular properties in several geometries, we may take advantage of the fact the molecular orbitals at the previous geometry probably is quite close to the optimized MOs at the new geometry, and thus restart from the MOs contained in the SIRIUS.RST file, as indicated in the following example:

**DALTON INPUT
.RUN WAVE FUNCTIONS
**WAVE FUNCTIONS
.HF
*ORBITAL INPUT
.MOSTART
 NEWORB
**END OF DALTON INPUT

Running DFT  calculations is very similar to Hartree-Fock, except for the specification of the functional: The .DFT keyword is followed by a line describing the functional to be used. The simple input below will start a B3LYP geometry optimization:

**DALTON INPUT
.OPTIMIZE
**WAVE FUNCTIONS
.DFT
 B3LYP
**END OF DALTON INPUT

We finish this list of examples with a high-spin open-shell DFT input. We need to specify the number of singly as well as doubly occupied orbitals in each symmetry in the **SCF INPUT section using the .SINGLY OCCUPIED and .DOUBLY OCCUPIED keywords respectively (here assuming $D_{2h}$ symmetry):

**DALTON
.RUN WAVE FUNCTIONS
**WAVE FUNCTION
.DFT
 B3LYP
*SCF INPUT
.DOUBLY OCCUPIED
 3 1 1 0 2 0 0 0
.SINGLY OCCUPIED
 0 0 0 0 0 1 1 0
**END OF DALTON INPUT

A complete list of available functionals can be found in the Reference Guide, see Sec. 24.2.7

The next input example gives the necessary input for a Complete Active Space SCF (CASSCF) calculation where we use MP2 to provide starting orbitals for our MCSCF. The active space may for instance be chosen on the basis of an MP2 natural orbital occupation analysis as described in Ref. [20]. The input would be:

**DALTON INPUT
.RUN WAVE FUNCTIONS
**WAVE FUNCTIONS
.HF
.MP2
.MCSCF
*SCF INPUT
.DOUBLY OCCUPIED
 2 0 0 0
*CONFIGURATION INPUT
.SYMMETRY
 1
.SPIN MULTIPLICITY
 1
.INACTIVE ORBITALS
 0 0 0 0
.ELECTRONS (active)
 4
.CAS SPACE
 6 4 4 0
**END OF DALTON INPUT

As for Hartree-Fock calculation, we may want to use available molecular orbitals on the SIRIUS.RST file from previous calculations as starting orbitals for our MCSCF as indicated in this input example:

**DALTON INPUT
.RUN WAVE FUNCTIONS
**WAVE FUNCTIONS
.MCSCF
*ORBITAL INPUT
.MOSTART
 NEWORB
*CONFIGURATION INPUT
.SYMMETRY
 1
.SPIN MULTIPLICITY
 1
.INACTIVE ORBITALS
 0 0 0 0
.ELECTRONS (active)
 4
.RAS1 SPACE
 2 1 1 0
.RAS2 SPACE
 2 2 2 0
.RAS3 SPACE
 6 4 4 2
.RAS1 ELECTRONS
 0 2
.RAS3 ELECTRONS
 0 2
*OPTIMIZATION
.TRACI
.FOCKONLY
**END OF DALTON INPUT

The next input describes the optimization of the first excited state of the same symmetry as the ground state. To speed up convergence, we employ optimal orbital trial vectors as described in Ref. [21]. Such an input would look like:

**DALTON INPUT
.RUN WAVE FUNCTIONS
**WAVE FUNCTIONS
.TITLE
4 2 2 0 CAS on first excited 1A_1 state, converging to 1.D-07
.MCSCF
.NSYM
  4
*CONFIGURATION INPUT
.SYMMETRY
  1                 | same symmetry as ground state
.SPIN MULTIPLICITY
  1
.INACTIVE ORBITALS
 1 0 0 0
.ELECTRONS (active)
 8
.CAS SPACE
 4 2 2 0
*ORBITAL INPUT
.MOSTART
 NEWORB
*CI VECTOR
.STARTHDIAGONAL    | compute start vector from Hessian CI-diagonal
*OPTIMIZATION
.THRESH
 1.D-07
.SIMULTANEOUS ROOTS
  2 2
.STATE
  2                 | 2 since the first exited state has the same symmetry
!                     as the ground state
.OPTIMAL ORBITAL TRIAL VECTORS
*PRINT LEVELS
.PRINTUNITS
 6 6
.PRINTLEVELS
 5 5
**END OF DALTON INPUT

The next input describes the calculation of a core-hole state of the carbon 1s orbital in carbon monoxide, the first example employing a frozen core:

**DALTON INPUT
.RUN WAVE FUNCTIONS
**WAVE FUNCTIONS
.TITLE
C1s core hole state of CO, 4 2 2 0 valence CAS + C1s.
Frozen core orbital calculation.
.MCSCF
.NSYM
  4
*CONFIGURATION INPUT
.SYMMETRY
  1
.SPIN MULTIPLICITY
  2                | Doublet spin symmetry because of opened core orbital
.INACTIVE ORBITALS
 2 0 0 0           | O1s and O2s orbitals are inactive while the
!                    opened core orbital, C1s, must be active
.ELECTRONS (active)
 9                 | All valence electrons plus the core hole electron
!                    are active
.RAS1 SPACE
 1 0 0 0           | The opened core orbital (NOTE: always only this orb.)
.RAS1 ELECTRONS
 1 1               | We impose single occupancy for the opened core orbital
.RAS2 SPACE
 4 2 2 0           | Same as the CAS space in the ground state calculation
*OPTIMIZATION
.COREHOLE
 1 2               | Symmetry of the core orbital and the orbital in this
!                    symmetry with the core hole according to list of input
!                    orbitals. The same thing could be obtained by
!                    reordering the core orbital to the first active orb.
!                    (by .REORDER), and specifying .FREEZE and .NEO ALWAYS
.TRACI
*ORBITAL INPUT
.MOSTART
 NEWORB            | Start from corresponding MCSCF ground state
*CI VECTOR
.STARTHDIAGONAL
**END OF DALTON INPUT

whereas we in a calculation where we would allow the core to relax only would require the following changes compared to the previous input, assuming that we start out from orbitals and CI vectors generated by the previous calculation .STARTHDIAGONAL is therefore replaced by .STARTOLDCI, and the core orbital has number 3 (instead of 1) in the list of orbitals in the first symmetry. " .CORERELAX" is specified for relaxation of the core orbital using the NR algorithm.

*OPTIMIZATION
.COREHOLE
 1 3
.CORERELAX
*CI VEC
.STARTOLDCI

This example describes calculations for non-equilibrium solvation, where the molecule will be enclosed in a spherical cavity. Usually one starts with a calculation of a reference state (most often the ground state) with equilibrium solvation, using keyword .INERSFINAL. The interface file is then used (without user interference) for a non-equilibrium excited state calculation; keyword .INERSINITIAL.

**DALTON INPUT
.RUN WAVE FUNCTIONS
**WAVE FUNCTIONS
.TITLE
 2-RAS(2p2p') : on F+ (1^D) in Glycol
.MCSCF
.NSYM
 8
*CONFIGURATION INPUT
.SPIN MULTIPLICITY
 1
.SYMMETRY
 1
.INACTIVE ORBITALS
 1  0  0  0  0  0  0  0
.ELECTRONS (active)
 6
.RAS1 SPACE
 0  0  0  0  0  0  0  0
.RAS2 SPACE
 1  2  2  0  2  0  0  0
.RAS3 SPACE
 8  4  4  3  4  3  3  1
.RAS1 ELECTRONS
 0  0
.RAS3 ELECTRONS
 0  2
*OPTIMIZATION
.NEO ALWAYS
.OPTIMAL ORBITAL TRIAL VECTORS
*ORBITAL INPUT
.MOSTART
 NEWORB
*CI VECTOR
.STARTOLDCI
*SOLVENT
.CAVITY
 2.5133D0
.INERSINITIAL     | initial state inertial polarization
 37.7D0  2.050D0  | static and optic dielectric constants for Glycol
.MAX L
 10
.PRINT
 6
**END OF DALTON INPUT