The initial orbital guess is either obtained by diagonalizing the bare nuclei Hamiltonian, from an initial guess produced by the module Guessorb or from orbitals of a previous HartreeFock SCF calculation. These starting orbitals are automatically located in the order
By default SCF behaves in different ways depending on what kind of start orbitals are found according to
One of the main objects of the SCF program in the context of the
MOLCAS program system is to generate starting
orbitals for subsequent MCSCF calculations.
Two options are available to
improve the canonical HartreeFock orbitals in this respect.
The SCF program requires the oneelectron integral file
ONEINT and the communications file RUNFILE,
which contains among others the
basis set specifications processed by SEWARD. For conventional
(not integraldirect) runs the twoelectron integral file ORDINT
is required as well. All these files are generated by a preceding
SEWARD run.

File  Contents 
SCFORB  SCF orbital output file. Contains the canonical HartreeFock orbitals for closed shell calculations. If the IVO option was specified, the virtual orbitals instead are those that diagonalize the bare nuclei Hamiltonian within that subspace. 
UHFORB  Contains the canonical HartreeFock orbitals for open shell calculations. 
UNAORB  This file is produced if you make a UHF calculation and it contain natural orbitals. 
MD_SCF  Molden input file for molecular orbital analysis. 
Below follows a description of the input to SCF.
The input for each module is preceded by its name like:
&SCF
Argument(s) to a keyword, either individual or composed by several entries, can be placed in a separated line or in the same line separated by a semicolon. If in the same line, the first argument requires an equal sign after the name of the keyword.
Keyword  Meaning  
TITLe  One line for the title  
UHF  Use this keyword to run Unrestricted HartreeFock code. Note that current implementation of UHF code has some restrictions, and not all features of SCF program are supported.  
ZSPIN  Use this keyword to specify the difference in the number of and electrons in the system. The default is 0 or 1 depending on if there is an even or odd number of electrons. Any value different from 0 requires the UHF keyword. This keyword is not needed when you specify the number of electrons with the keyword OCCUpied.  
SPIN  Alternative way of specifying the electronic spin of the system. The keyword is followed by an integer giving the value of spin multiplicity (2S+1). Default is 1 (singlet) or 2 (doublet) depending on if there is an even or odd number of electrons. Any value different from 1 requires the UHF keyword.  
KSDFT  Use this keyword to do density functional theory calculations. This keyword should be followed by functional keyword: BLYP, B3LYP, B3LYP5, HFB, HFS, LDA, LDA5, LSDA, LSDA5, SVWN, SVWN5, TLYP, PBE, PBE0, M06, M062X, M06HF, M06L. Example: KSDFT=B3LYP  
DFCF  Use this optional keyword to scale the exchange terms and/or correlation terms of the density functional requested with KSDFT. This keyword should be followed by the scaling factor for the exchange terms and the scaling factor for the correlation terms, separated by a space. If the values are 1.0 (default), then the original density functional is used. For an HLEtype functional, use 1.25 (for exchange) and 0.5 (for correlation). Example: DFCF=1.25 0.5  
CHARge  Use this keyword to set the number of electrons in the system.
This number is defined by giving the net charge of the system.
If this keyword is not specified, the molecule is assumed to
have net charge zero.
The input is given as
Charge=n where n is the charge of the system.
 
OCCUpied  Use this keyword to set the number of electrons in the system.
This number is defined by giving the number of electron pairs
per irreducible representation of the subgroup of D_{2h} used
in the calculation.
You can use one and only one of the keywords,
CHARge and
OCCUpied for this purpose.
If neither of these keywords are specified
CHARge is assumed with a net charge of zero.
It should be noted that the ``fermi aufbau''
procedure is not used when you specify this keyword.
The input for one of the point groups D_{2}, C_{2h} or C_{2v}
is given as
OCCUpied= n1 n2 n3 n4 where n1 is the number of electron pairs (occupied orbitals)
in the first irreducible representation, etc.
If UHF keyword was specified, occupation numbers must be specified in two lines: for alpha and beta spins  
FERMi  Use this keyword to specify that you want to use the ``Fermi aufbau''
procedure for the first few iterations to ensure convergence.
The orbitals will be partially populated according to a Fermi
population.
The input is gives as
Fermi= m where m is the temperature parameter according to
 
CHOLesky  SCF will use Cholesky (or RI/DF) representation of the twoelectron integrals to compute the corresponding contributions to the Fock or KS matrices. The default (LK) algorithm is used. The configuration may be tailored using the ChoInput section. Default is to not use Cholesky unless the Cholesky (or RI/DF) representation of the twoelectron integrals has been produced by SEWARD.  
CHOInput  This marks the start of an input section for modifying
the default settings of the Cholesky SCF.
Below follows a description of the associated options.
The options may be given in any order,
and they are all optional except for
ENDChoinput which marks the end of the CHOInput section.
 
CONStraints  Performs a Constrained (Natural Orbitals) SCF calculation, available only in combination with Cholesky or RI integral representation.
An example of input for the keyword CONS is the following:
CONStraints 2 3 1 1 1 1 1 ADDCorrelation pbe SAVErage The keyword CONS has two compulsory arguments: the number of constrained NOs (in each irrep) to be used in the CNOSCF calculation, followed by one line per irrep specifying the spin configuration of the socalled (+) wavelet (1 –> beta, 1 –> alpha) The OPTIONAL keyword ADDC is used to include a correlation energy correction through a DFT functional specified as argument (LDA, LDA5, PBE and BLYP available at the moment) The OPTIONAL keyword SAVE forces the program to use spinaveraged wavelets.  
OFEMbedding  Performs a OrbitalFree Embedding (OFE)SCF calculation, available only in combination with Cholesky or RI integral representation.
The runfile of the environment subsystem renamed AUXRFIL is required.
An example of input for the keyword OFEM is the following:
OFEMbedding ldtf/pbe dFMD 1.0 1.0d2 FTHAw 1.0d4 The keyword OFEM requires the specification of two functionals in the form fun1/fun2, where fun1 is the functional used for the Kinetic Energy (available functionals: ThomasFermi, with acronym LDTF, and the NDSD functional), and where fun2 is the xcfunctional (LDA, LDA5, PBE and BLYP available at the moment). The OPTIONAL keyword dFMD has two arguments: first, the fraction of correlation potential to be added to the OFE potential (zero for KSDFT and one for HF); second, the exponential decay factor for this correction (used in PES calculations). The OPTIONAL keyword FTHA is used in a freezeandthaw cycle (EMIL Do While) to specify the (subsystems) energy convergence threshold.  
ITERations  Specifies the maximum number of iterations. The default is 400 which
is also the largest number you can specify.
 
CORE  The starting vectors are obtained from a diagonalization of the core Hamiltonian.  
LUMORB  The starting vectors are taken from a previous SCFORB file called INPORB.  
FILEORB  The starting vectors are taken from a previous SCFORB file, specified by user.  
GSSRunfile  The starting vectors are taken from the orbitals produced by Guessorb.  
HLGAp  This keyword is used to make the program level shift the virtual orbitals in such a way that the HOMO LUMO gap is at least the value specified on the next line. This will help convergence in difficult cases but may lead to that it converges to an excited configuration. A suitable value is 0.2. 
Keyword  Meaning 
SCRAmble  This keyword will make the start orbitals slightly scrambled, accomplished by making a few small random orbital rotations. How much the orbitals are scrambled is determined by the parameter read on the next entry. A reasonable choice for this parameter is 0.2 which correspond to maximum rotation angle of . Using this keyword may be useful for UHF calculations with same number of and electrons that are not closed shell cases. 
ORBItals  Specifies the number of orbitals in the subspace of the full orbital space defined by the basis set, in which the SCF energy functional is optimized. The size of this subspace is given for each of the irreducible representations of the subgroup of D_{2h}. If this keyword is not specified when starting orbitals are read, the full orbital space is assumed. The keyword takes as argument nIrrep (# of irreps) integers. Note that this keyword is only meaningful when the SCF program is fed with input orbitals (cf. LUMORB). 
FROZen  Specifies the number of orbitals not optimized during iterative procedure. The size of this subspace is given for each of the irreducible representations of the subgroup of D_{2h}. If this keyword is not specified the number of frozen orbitals is set to zero for each irreducible representation. If the starting vectors are obtained from a diagonalization of the bare nuclei Hamiltonian the atomic orbitals with the lowest oneelectron energy are frozen. If molecular orbitals are read from INPORB the frozen orbitals are those that are read in first in each symmetry. The keyword takes as argument nIrrep (# of irreps) integers. 
OVLDelete  Specifies the threshold for deleting near linear dependence in the basis set. The eigenvectors of the overlap matrix with eigenvalues less than that threshold are removed from the orbital subspace, and do not participate in the optimization procedure. The default value is 1.0d5. The keyword takes as argument a (double precision) floating point number. Note that the SCFORB file will contain the deleted orbitals as a complementary set to the actual SCF orbitals! In future use of this orbital file the complementary set should always be deleted from use. 
PRORbitals  Specifies which orbitals are to be printed in the log file (standard output).
The keyword takes as argument two integers.
The possible values are:
Second (optional) argument specifies a format:

PRLScf  Specifies the general print level of the calculation. An integer has to be supplied as argument. The default value, 1, is recommended for production calculations. 
ROBU  Robust LDF integral representation (nonhybrid KSDFT only). Requires Local Density Fitting (LDF) in SEWARD. This is the default for LDF. 
NR2  Nonrobust LDF integral representation with 2index integrals only (nonhybrid KSDFT only). Requires Local Density Fitting (LDF) in SEWARD. Default is robust integral representation. 
NR3  Nonrobust LDF integral representation with 3index integrals only (nonhybrid KSDFT only). Requires Local Density Fitting (LDF) in SEWARD. Default is robust integral representation. 
XIDI  Use exact integral diagonal blocks with LDF. Reduces the risk of negative eigenvalues of the approximate integral matrix. Default is to not use exact integral diagonal blocks. 
THREsholds  Specifies convergence thresholds. Four individual thresholds are specified as arguments, which have to be fulfilled simultaneously to reach convergence: EThr, DThr and FThr specify the maximum permissible difference in energy, density matrix elements and Fock matrix elements, respectively, in the last two iterations. The DltNTh finally specifies the norm of the orbital displacement vector used for the orbital rotations in the secondorder/C^{2}DIIS procedure. The corresponding values are read in the order given above. The default values are 1.0d9, 1.0d4, 1.5d4, and 0.2d4, respectively. Note that these thresholds automatically define the threshold used in the direct Fock matrix construction to estimate individual contributions to the Fock matrix such that the computed energy will have an accuracy that is better than the convergence threshold. 
NODIis  Disable the DIIS convergence acceleration procedure. 
DIISthr  Set the threshold on the change in density, at which the DIIS procedure is turned on. The keyword takes as argument a (double precision) floating point number. The default value is 0.15. 
QNRThr  Set the threshold on the change in density, at which the
secondorder/C^{2}DIIS
procedure kicks in.
The keyword takes as argument a (double precision) floating point number.
The default value is 0.15.
Note: the change in density has to drop under both the DIISthr and the QNRThr threshold, for the secondorder/C^{2}DIIS to be activated. If the latter is set to zero the older first order C^{2}DIIS procedure will be used instead. 
C1DIis  Use C^{1}DIIS for convergence acceleration rather than C^{2}DIIS which is the default (not recommended). 
NODAmp  Disable the Damping convergence acceleration procedure. 
OCCNumbers  Gives the option to specify occupation numbers other than 0 and 2. This can be useful for generating starting orbitals for open shell cases. It should be noted however, that it is still the closed shell SCF energy functional that is optimized, thus yielding unphysical energies. Occupation numbers have to be provided for all occupied orbitals. In the case of UHF calculation occupation numbers should be specified on two different entries: for alpha and beta spin. 
IVO  Specifies that the virtual orbitals are to be improved for subsequent MCSCF calculations. The core Hamiltonian is diagonalized within the virtual orbital subspace, thus yielding as compact orbitals as possible with the constraint that they have to be orthogonal to the occupied orbitals. Note that this option must not be used whenever the HartreeFock wavefunction itself is used as a reference in a subsequent calculation. 
NOMInimization  Program will use density differences rather than minimized differences. 
ONEGrid  Disable use of a smaller intermediate grid in the integration of the DFT functional during the first SCF iterations. 
RFPErt  This keyword will add a constant reaction field perturbation to the bare nuclei hamiltonian. The perturbation is read from RUNOLD (if not present defaults to RUNFILE) and is the latest self consistent perturbation generated by one of the programs SCF or RASSCF. 
STAT  This keyword will add an addition print outs with statistic information.

For calculations of a molecule in a reaction field see section of the present manual and section of the examples manual.
Keyword  Meaning  
LSDA, LDA, SVWN  Vosko, Wilk, and Nusair 1980 correlation functional fitting the RPA solution to the uniform electron gas [100] (functional III in the paper).  
LSDA5, LDA5, SVWN5  Functional V from the VWN80 paper [100] which fits the CeperleyAlder solution to the uniform electron gas.  
HFB  Becke's 1988 exchange functional which includes the Slater exchange along with corrections involving the gradient of the density [101].  
HFS  with the theoretical coefficient of 2/3 also known as Local Spin Density exchange [102,103,104].  
HFB86  Becke's 1986 twoparameter exchange functional which includes the Slater exchange along with corrections involving the gradient of the density [105,106].  
HFO  Handy's standalone OPTX exchange functional [107]  
BLYP  Becke's 1988 exchange functional which includes the Slater exchange along with corrections involving the gradient of the density [101]. Correlation functional of Lee, Yang, and Parr, which includes both local and nonlocal terms [108,109].  
BPBE  Becke's 1988 exchange functional which includes the Slater exchange along with corrections involving the gradient of the density [101] , combined with the GGA correlation functional by Perdew, Burke and Ernzerhof [110]  
B3LYP  Becke's 3 parameter functional [111] with the form
 
B3LYP5  Becke's 3 parameter functional [111] with the form
 
B2PLYP  Grimme's doublehybrid density functional [112] based on Becke;s 1988 exchange and LYP correlation GGA functionals with the form
 
B86LYP  Becke's 1986 exchange [105,106] functional combined with the LYP correlation [108,109]  
BWig  Becke's 1988 GGA exchange functional combined with the local Wigner correlation functional [113]  
GLYP  Gill's 1996 GGA exchange functional [114] combined with the combined with the LYP correlation [108,109]  
OLYP  Handy's OPTX exchange functional [107] combined with the LYP correlation [108,109]  
OPBE  Handy's OPTX exchange functional [107] combined with the PBE correlation[110]  
O3LYP  A hybrid density functional based on the OPTX exchange [115] , with the form
 
KT3  The exchangecorrelation functional by Keal and Tozer, 2004 [116,117]  
TLYP 
where the nonlocal correlation functional is the LYP functional  
PBE  The Perdew, Burke, Ernzerhof GGA functional 1996 [110].  
PBE0  The Perdew, Ernzerhof, Burke nonempirical hybrid functional 1996 [118].  
PBEsol  The Perdew et al. 2008 modification of PBE for solids  
RGE2  The regularized gradient approximation (RGE2 )exchange functional by Ruzsinszky, Csonka, and Scuseria, 2009 that contains higherpower s terms in the exchange functional, as compared to the PBEsol. It is coupled with the PBEsol correlation [119]  
PTCA  The correlation functional by Tognetti, Cortona, and Adamo combined with the PBE exchange [120]  
SSB  The exchange functional SSBsw by Swart, Sola, and Bickelhaupt, 2008 [121] that switches between the OPTX exchange for small values of the reduced density gradient and the PBE exchange for the large ones. It is combined with the PBE correlation functional.  
M06  The M06 functional of the Minnesota 2006 class of functionals by Zhao and Truhlar [122,123,124,125]  
M06L  The M06L functional of the Minnesota 2006 class of functionals by Zhao and Truhlar [122,123,124,125]  
M06HF  The M06HF functional of the Minnesota 2006 class of functionals by Zhao and Truhlar [122,123,124,125]  
M062X  The M062X functional of the Minnesota 2006 class of functionals by Zhao and Truhlar [122,123,124,125] 
Keyword  Meaning 
CONVentional  This option will override the automatic choice between the conventional and the direct SCF algorithm such that the conventional method will be executed regardless of the status of the ORDINT file. 
DISK  This option enables/disables the semidirect algorithm. It requires two arguments which specifies the max Mbyte of integrals that are written on disk during the first iteration (and retrieved later in subsequent iterations) and the size of the corresponding I/O buffer in kbyte. The default values are 2000 MByte and 512 kByte. In case the specified disk space is zero and the I/O buffer is different from zero it will default to a semidirect SCF with incore storage of the integrals. The size of the memory for integrals storage is the size of the I/O buffer. If the size of the disk is nonzero and the I/O buffer size is zero the latter will be reset to the default value. 
THIZe  This option specifies a threshold for twoelectron integrals. Only integrals above this threshold (but not necessarily all of those) are kept on disk for the semidirect algorithm. The keyword takes as argument a (double precision) floating point number. 
SIMPle  If this option is specified, only a simple prescreening scheme, based solely on the estimated twoelectron integral value will be employed (no density involved). 
First we have the bare minimum of input. This will work well for almost all systems containing an even number of electrons.
&SCF
The next example is almost as simple. Here we have an open shell case, i.e. you have an odd number of electrons in the neutral system and you need to generate starting orbitals for RASSCF. In this case we recommend that you perform a calculation on the cation with the input below.
&SCF; Charge= 1
The next example explains how to run UHF code for a nitrogen atom:
&SCF; UHF; ZSPIN=3
The next example is a bit more elaborate and show how to use a few of the keywords. The system is water that have the electron configuration .
&SCF; Title= Water molecule. Experimental equilibrium geometry. The symmetries are a1, b2, b1 and a2.
Occupied= 3 1 1 0
Threshold= 0.5D9 0.5D6 0.5D6 0.5D5
* semidirect algorithm writing max 128k words (1MByte) to disk
* the size of the I/O buffer by default (512 kByte)
Disk= 1 0
Ivo