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Table of contents

• Table of contents
• Details
• Keywords
  • The REFERENCE Keyword
    • DFT Functionals
  • The NUCREFERENCE Keyword
  • NEO-DFT Functionals
  • The JOB Keyword
  • The X2CTYPE Keyword
  • The ATOMICX2C Keyword
  • The SPINORBITSCALING Keyword
• PROTQM Section
• Examples
  • Restricted Hartree-Fock Energy
  • Unrestricted Kohn-Sham (B3LYP) Response
  • Complex Generalized Kohn-Sham (LSDA) Energy
  • Relativistic Kohn-Sham (BHandH) Electron Dynamics

Details

The QM section handles the reference and ChronusQ job type specification. The QM section is a required section for all ChronusQ jobs.

Keywords

The REFERENCE Keyword

The QM.REFERENCE keyword allows for specification of the reference wave function for SCF and post-SCF ChronusQ calculations. ChronusQ currently supports Hartree-Fock and Kohn-Sham reference choices. The REFERENCE keyword may be constructed systematically as

REFERENCE = [ REAL/COMPLEX ] <R/RO/U/G/2C><HF/FUNCTIONAL>

The REAL/COMPLEX specification is optional, and a canonical choice will be chosen for the user should it not be specified (COMPLEX for 2-Component / GIAO references, REAL otherwise). The second two keyword fields in the above template are required, and may be combined freely.

R/RO/U/G/X2C specifies the desired spin symmetry of the reference wave function: Restricted (S² eigenfunction, even number of particles), Restricted Open (S² eigenfunction, any number of particles), Unrestricted (S_z eigenfunction), Generalized (2-Component, no spin symmetry), X2C (deprecated, "Exact" 2-Component Relativistic, with one-body spin-orbit coupling, no spin symmetry), respectively.

HF will generate a Hartree-Fock wave function, and FUNCTIONAL is a place holder to specify a Kohn-Sham wave function with the FUNCTIONAL DFT functional. (See below) RO is currently only compatible with HF, not Kohn-Sham.

DFT Functionals

ChronusQ supports the following DFT functionals (10/9/2020):

Addition of more functionals is possible - if a specific functional is required for your research, please open an issue!

The NUCREFERENCE Keyword

The QM.REFERENCE keyword allows for specification of the reference wave function for quantum nuclei in the SCF and post-SCF ChronusQ procedures. Currently both NEO-HF and NEO-DFT wavefunction options are available. It is assumed that systems occupy high-spin configurations, so by convention unrestricted wavefunctions should be used. Note that Generalized and X2C options are not currently implemented for NEO methods.

REAL/COMPLEX specification is optional as with QM.REFERENCE, but NEO wavefunctions must match the type of the electronic reference (only REAL/REAL or COMPLEX/COMPLEX for REF/NUCREF are allowed).

HF will generate a respective NEO-HF wavefunction, while quantum-nuclear functionals have the same conventions as their electronic counterparts. Currently implemented functionals are listed below.

NEO-DFT Functionals

The JOB Keyword

The JOB keyword controls the type of calculation done by ChronusQ. The currently supported job types are:

For more information, see the respective input sections of each.

The X2CTYPE Keyword

When the reference is specified as X2C, different methodologies can be used to define the transformation between the four- and two-component Hamiltonians. The X2CTYPE keyword controls the type of transform used.

The ATOMICX2C Keyword

When the X2CTYPE keyword is specified as SPINFREE or ONEE, either a standard molecular X2C transformation is performed, or local approximations can be utilized. The following options control the types of local approximation.

The SPINORBITSCALING Keyword

When the reference is specified as X2C, different methodologies can be used to artificially include the two-electron spin-orbit effect. The SPINORBITSCALING keyword switches such scaling.

PROTQM Section

For NEO calculations, a second section needs to be included that designates the PROTQM options. Since JOB is specified previously, only reference information needs to be included. The same conventions mentioned previously apply here. GIAO and relativistic options are not yet implemented for nuclear wavefunctions. Below is the list of keywords needed for this section.

Examples

Restricted Hartree-Fock Energy

[QM]
Reference = RHF
Job = SCF

Unrestricted Kohn-Sham (B3LYP) Response

[QM]
Reference = UB3LYP
Job = Resp

Complex Generalized Kohn-Sham (LSDA) Energy

[QM]
Reference = Complex GLSDA
Job = SCF

Relativistic Kohn-Sham (BHandH) Electron Dynamics

[QM]
Reference = X2CBHandH
Job = RT