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  • QM

Last edited by Ben Link May 12, 2022
Page history

QM

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

Keyword Type Description Default Required
REFERENCE String Type of reference wavefunction N/A Yes
NUCREFERENCE String Type of NEO reference wavefunction N/A No
JOB String Type of calculation N/A Yes
X2CTYPE String Type of X2C transformation DEFAULT No
ATOMICX2C String Type of Atomic X2C transformation OFF No
SPINORBITSCALING String Type of spin-orbit scaling technique DEFAULT No

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 (Sz 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):

Name Type Description
SLATER Pure LDA Exchange Slater exchange
LSDA/LDA Pure LDA Exchange/Correlation Slater exchange + VWN3 correlation
SVWN5 Pure LDA Exchange/Correlation Slater exchange + VWN5 correlation
B88 Pure GGA Exchange B88 exchange
BLYP Pure GGA Exchange/Correlation B88 exchange + LYP correlation
PBEXPBEC Pure GGA Exchange/Correlation PBE exchange + PBE correlation
B3LYP Hybrid GGA Exchange/Correlation B3LYP functional
B3PW91 Hybrid GGA Exchange/Correlation B3PW91 functional
PBE0 Hybrid GGA Exchange/Correlation PBE0 functional
BHANDHLYP Hybrid GGA Exchange/Correlation BHandHLYP functional
BHANDH Hybrid GGA Exchange/Correlation BHandH functional

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

Name Type Description
epc17-2 NEO-LDA-like Functional Quantum electron-proton correlation functional
epc19 NEO-GGA-like Functional Quantum electron-proton correlation with density gradient included

The JOB Keyword

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

Value Description
SCF Self-consistent orbital optimization
RESP Response theory
RT Electron dynamics

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.

Value Description
OFF Turns off X2C
ONEELECTRON/ONEE The standard core-Hamiltonian X2C transformation algorithm
SPINFREE One-electron X2C, but only include scalar relativistic effect
FOCK X2C transformation based on the four-component Fock matrix
DEFAULT ONEE in case of x2c reference, OFF otherwise.

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.

Value Description
OFF The standard X2C transformation algorithm without local approximation
ALH Atomic local approximation to the Hamiltonian
ALU Atomic local approximation to the transformation matrix
DLH Diagonal local approximation to the Hamiltonian
DLU Diagonal local approximation to the transformation matrix

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.

Value Description
NOSCALING Turns off two-electron spin-orbit scaling
BOETTGER The Boettger factor scaling technique
ATOMICMEANFIELD/AMFI Atomic mean-field two-electron spin-orbit effect
DEFAULT BOETTGER in case of one-electron spin-orbit X2C calculation, NOSCALING otherwise.

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.

Keyword Type Description Default Required
REFERENCE String Type of reference wavefunction N/A Yes

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
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Overview and Features

Getting ChronusQ

Running ChronusQ

Input sections

     Overview
     QM and PROTQM
     Molecule
     Basis and DFBasis
     Ints
     DFTInts
     SCF
     RT
     Response
     CC
     MCSCF
     Misc

FAQ

Examples

     HF energy
     Relativistic DFT Energy
     Linear Response TDDFT
     Frequency dependent TDHF
     Model Order Reduction of TDDFT
     Electron dynamics

Keyword Reference

Binary Reference