Table of contents
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 
REFERENCE
Keyword
The 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^{2} eigenfunction, even number of particles), Restricted Open (S^{2} eigenfunction, any number of particles), Unrestricted (S_{z} 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!
NUCREFERENCE
Keyword
The 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 
JOB
Keyword
The 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.
X2CTYPE
Keyword
The 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. 
ATOMICX2C
Keyword
The 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 
SPINORBITSCALING
Keyword
The 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