

## Table of contents






[[_TOC_]]






## 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 spinorbit scaling technique  `DEFAULT`  No 






### The `REFERENCE` Keyword






The `QM.REFERENCE` keyword allows for specification of the reference wave function for SCF and postSCF ChronusQ calculations. ChronusQ currently supports HartreeFock and KohnSham 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 2Component / 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 (S<sup>2</sup> eigenfunction, even number of particles), Restricted Open (S<sup>2</sup> eigenfunction, any number of particles), Unrestricted (S<sub>z</sub> eigenfunction), Generalized (2Component, no spin symmetry), X2C (deprecated, "Exact" 2Component Relativistic, with onebody spinorbit coupling, no spin symmetry), respectively.






`HF` will generate a HartreeFock wave function, and `FUNCTIONAL` is a place holder to specify a KohnSham wave function with the `FUNCTIONAL` DFT functional. (See below) **`RO` is currently only compatible with `HF`, not KohnSham.**






#### 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!](https://urania.chem.washington.edu/chronusq/chronusq_public//issues)






### The `NUCREFERENCE` Keyword






The `QM.REFERENCE` keyword allows for specification of the reference wave function for quantum nuclei in the SCF and postSCF ChronusQ procedures. Currently both NEOHF and NEODFT wavefunction options are available. It is assumed that systems occupy highspin 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 NEOHF wavefunction, while quantumnuclear functionals have the same conventions as their electronic counterparts. Currently implemented functionals are listed below.






### NEODFT Functionals






 Name  Type  Description 



     



 epc172  NEOLDAlike Functional  Quantum electronproton correlation functional 



 epc19  NEOGGAlike Functional  Quantum electronproton 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`  Selfconsistent 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 twocomponent Hamiltonians. The `X2CTYPE` keyword controls the type of transform used.






 Value  Description 



    



 `OFF`  Turns off X2C 



 `ONEELECTRON`/`ONEE`  The standard coreHamiltonian X2C transformation algorithm 



 `SPINFREE`  Oneelectron X2C, but only include scalar relativistic effect 



 `FOCK`  X2C transformation based on the fourcomponent 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 twoelectron spinorbit effect. The `SPINORBITSCALING` keyword switches such scaling.






 Value  Description 



    



 `NOSCALING`  Turns off twoelectron spinorbit scaling 



 `BOETTGER`  The Boettger factor scaling technique 



 `ATOMICMEANFIELD`/`AMFI`  Atomic meanfield twoelectron spinorbit effect 



 `DEFAULT`  `BOETTGER` in case of oneelectron spinorbit 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 HartreeFock Energy






```



[QM]



Reference = RHF



Job = SCF



```






### Unrestricted KohnSham (B3LYP) Response






```



[QM]



Reference = UB3LYP



Job = Resp



```






### Complex Generalized KohnSham (LSDA) Energy



```



[QM]



Reference = Complex GLSDA



Job = SCF



```






### Relativistic KohnSham (BHandH) Electron Dynamics



```



[QM]



Reference = X2CBHandH



Job = RT



``` 


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