Table of contents
 Table of contents
 Details
 Keywords Summary
 The JobType Keyword
 Keywords to partition correlation space
 Keywords to control CI diagonalization
 Keywords to control orbital rotations
 Other Keywords
 Example
 Citations
Details
The MCSCF
section handles the MultiConfigurational SelfConsistent Field parameters for solving the multireference configuration interactions and the optimization of the multiconfigurational wave functions.
Keywords Summary
Keyword  Type  Description  Default  Required 

JobType  String  A specific MCSCF job  N/A  Yes 
NRoots  Integer  Number of states to compute  1  No 
StateAverage  bool  Use state average density for orbital rotation if true  true  No 
NActO  Integer(s)  Number of active orbitals  N/A  Yes 
NActE  Integer  Number of active electrons  N/A  Yes 
RAS1MaxHole  Integer  Maximum number of holes allowed in RAS1  N/A  if RAS 
RAS3MaxElec  Integer  Maximum number of electrons allowed in RAS1  N/A  if RAS 
CASOrbital  integer(s)  CAS Orbitals IDs  N/A  No 
RAS1Orbital  integer(s)  RAS1 orbitals IDs  N/A  No 
RAS2Orbital  integer(s)  RAS2 orbitals IDs  N/A  No 
RAS2Orbital  integer(s)  RAS3 orbitals IDs  N/A  No 
INOrbital  integer(s)  Inactive core orbitals IDs  N/A  No 
FVOrbital  integer(s)  frozen virtual orbitals IDs  N/A  No 
SwapMO  Multiline string  Swap ordering of MOs before MCSCF computations  N/A  No 
CIDiagAlg  String  Diagonalization algorithm to solve CI  FullMatrix  No 
MaxCIIter  integer  Maximum number of CI iterations in Davidson  128  No 
CIConv  Double precision float  Convergence threshold for CI vectors in Davidson  10^{6} 
No 
SCFAlg  String  Algorithm to do orbital rotation  AQ2nd  No 
MaxSCFIter  integer  Maximum number of SCF iterations (orbital rotation)  128  No 
SCFEneConv  Double precision float  Convergence threshold for state energies during orbital rotation  10^{8} 
No 
SCFGradConv  Double precision float  Convergence threshold for orbital gradient during orbital rotation  10^{4} 
No 
HessDiagScale  Double precision float  Scale factor for orbitalorbital Hessian  2.0  No 
OsciStren  integer  Compute oscillator strength among transitions of all states to first N number of states  0  No 
GenIVO  bool  Generate improved virtual orbitals if true  false  No 
JobType
Keyword
The The JobType
keyword basically specifies the intended computation in the input file, and keywords not related to the specified JobType
will be ignored. Currently available JobType
s includes:

CASCI
: complete active space configuration interactions. 
CASSCF
: complete active space self consistent field. 
RASCI
: restricted active space configuration interactions. 1CRASCI and usingFullMatrix
is not implemented.
Keywords to partition correlation space
NActO
and NActE
Keywords
The NActO
defines the number of active orbitals. For CAS
jobs, it need only one number, and for RAS
jobs, it need three numbers (separated by space) to specify number of orbitals in RAS1, RAS2, and RAS3.
NActE
defines the number of total active electrons, it only needs 1 number regardless CAS
or RAS
jobs. For RAS
jobs, RAS1 and RAS3 are assumed occupied and empty at ground state configurations
RAS1MaxHole
and RAS3MaxElec
Keywords
The RAS1MaxHole
and RAS3MaxElec
are need to define the maximum excitation levels for RAS
jobs.
*Orbital
Keywords
The The *Orbital
Keywords (CASOrbital
, RAS1Orbital
, RAS2Orbital
, RAS2Orbital
, INOrbital
FVOrbital
) can be used to select orbital groups using MO id numbers. Valid expression includes:
 multiple numbers separated by space or comma
,
 a range using two numbers connected by dash

One or more of those keywords can be specified together, with the requirement that the total number of orbitals are same as specified by NActO
. The orbital space will be partitioned using the explicit specified groups first, and then rest of the ungrouped orbitals will be partitioned in the order of IN, CAS, FV for CAS
jobs and IN, RAS1, RAS2, RAS3, FV for RAS
jobs.
for example:
 An
CAS
job with 20 MOs and 10 electrons in total and the following inputs
[MCSCF]
...
NActO = 6
NActE = 3
CASOrbital = 4,6, 912
...
will results as:
 inactive core orbitals (7 in total) as MO 1, 2, 3, 5, 7 ,8, 13
 active space orbitals (6 in total) as MO 4, 6, 9, 10, 11, 12
 frozen core orbitals as MO 14, 15, 16, 17, 18, 19, 20.
SwapMO
Keyword
The Same as SCF.SwapMO. Unlike SCF.SwapMO is doing swapping before SCF, MCSCF.SwapMO does swapping after SCF procedure but before MCSCF computations.
Keywords to control CI diagonalization
CIDiagAlg
Keyword
The The CIDiagAlg
keyword specifies the algorithm to diagonalize CI Hamiltonian. Available options now include:

FullMatrix
: form full CI matrix in core and then use BLAS function to perform diagonalization. This option is not implemented forRAS
jobs at this moment. 
Davidson
: use davidson algorithm to iteratively diagonalize the lowestNRoots
number of states. This is very usefully where only ground state and a few excited states are of interest in large CI calculations. Note that whenNRoots
is larger than half of the total number of configurations,Davidson
is actually slower thanFullMatrix
.
MaxCIIter
and CIConv
Keywords
The The MaxCIIter
and CIConv
keywords are only used in Davidson
algorithm. CIConv
is measured by the norm of CI vector residues.
Keywords to control orbital rotations
SCFAlg
Keyword
The The SCFAlg
keyword specifies the algorithm to do orbital rotations using Newton Raphson approach. Available options now include:

AQ2nd
: Approximated Quasisecond order method. The orbitalorbital Hessian matrix is approximated with diagonal onebody terms.
A few more options are under construction

Q2nd
: Quasisecond order method. The orbitalorbital Hessian matrix is approximated with exact diagonal terms. 
2nd
: Second order method. The full orbitalorbital Hessian matrix is constructed and inversed to construct rotation matrix.
MaxSCFIter
, SCFEneConv
and SCFGradConv
Keywords
The Use to control orbital rotation iterations. Program finishes when both energy change and gradient change meet the threshold defined by SCFEneConv
and SCFGradConv
.
HessDiagScale
Keyword
The Use to scale Hessian diagonal elements when doing orbital rotation, and it's only valid for AQ2nd
and Q2nd
. A larger HessDiagScale
will result in a smaller step size during orbital rotations. Sometimes, it helps convergence when using those approximated Hessians.
Other Keywords
OsciStren
KeyWord
The Request oscillator strength calculations between computed CI states. Input is an integer N
, and transitions of all states to the first N
number of states will be computed. Currently only two component calculations are supported.
GenIVO
KeyWord
The Whether to generate improved virtual orbitals after MCSCF completes. Virtual block Fock matrix, with contribution coming from a 'cationic' active space (electron density scaled by \frac{n_{e}  1}{n_{e}}
), is diagonalized to form a less diffusive virtual orbitals. This is useful and recommended for truncating virtual orbitals in a latter MRCI or RASCI calculations.
Example
CAS(3,8)CI with solving lowest 6 roots
[MCSCF]
JobType = CASCI
NActO = 8
NActE = 3
NRoots = 6
SA6CAS(3,8)SCF with state averaging on lowest 6 roots
[MCSCF]
JobType = CASSCF
NActO = 8
NActE = 3
NRoots = 6
StateAverage = true
RAS(11,26)(2,8,2,10)CISD with solving lowest 6 roots
[MCSCF]
JobType = RASCI
NActO = 8 8 10
NActE = 3
NRoots = 6
RAS1MaxHole = 2
RAS3MaxElec = 2
CIDiagAlg = Davidson
Citations

Andrew J. Jenkins, Hongbin Liu, Joseph M. Kasper, Michael J. Frisch, and Xiaosong Li (2019). Variational Relativistic TwoComponent CompleteActiveSpace SelfConsistent Field Method Journal of Chemical Theory and Computation, 2019, 15, 5, 2974–2982.

Hang Hu, Andrew J. Jenkins, Hongbin Liu, Joseph M. Kasper, Michael J. Frisch, and Xiaosong Li (2020). Relativistic TwoComponent Multireference Configuration Interaction Method with Tunable Correlation Space Journal of Chemical Theory and Computation, 2020, 16, 5, 2975–2984.