# Variables

Data may be stored in variables. A variable can be of type string, real or logical, depending on the type of the expression in its definition. Any sequence of characters which is not recognized as expression or variable is treated as string. In this section, we will discuss only real and logical variables. String variables will be discussed in more detail in section string variables. Variables can be used anywhere in the input, but they can be set only outside the input blocks for specific programs. For example, if a variable is used within the input block for HF, it must have been set before the HF{...}  input block.

Molpro automatically stores various results and data in system variables (see section variables set by the program), which can be used for further processing. A new feature of Molpro2002 is that most system variables are write protected and cannot be overwritten by the user. The input is automatically checked before the job starts, and should a system variable be set in the input the job will stop immediately with an error message. Only in some exceptions (see section system variables), system variables can be modified using the SET command (but not with the simple NAME=value syntax). Note that due to the changed usage and syntax of the SET command, compatibility with Molpro92 input syntax is no longer maintained.

A variable can be defined using

variable1=value1, variable2=value2, …

A variable definition is recognized by the equals sign in the first field of the input card. For example,

THRESH,ENERGY=1.d-8,GRADIENT=1.d-5

does not define variables; here ENERGY and GRADIENT are options for the THRESH directive.

Variables can have different types:

• Numbers: The value is a number or an expression. The general form of value is

expression [,] [unit]
unit is an optional string which can be used to associate a unit to the value. ANG[STROM], DEGREE, HARTREE are examples. Undefined variables in expressions are assumed to be zero (and defined to be zero at the same time).

• Logicals: The value can be .TRUE. or .FALSE. (.T. and .F. also work), or a logical expression. Internally, .TRUE. is stored as 1 and .FALSE. as zero.
• Strings: The value can either be a string enclosed in quotes or a string variable. See section string variables for more details.

Variables can be indexed, but only one-dimensional indexing is available. Indexed variables can be defined either individually, e.g.

R(1)=1.0 ANG
R(2)=1.2 ANG
R(3)=1.3 ANG

or as a vector of values enclosed by square brackets:

R=[1.0,1.1,1.2] ANG

Subranges can also be defined, e.g.

R(1)=1.0 ANG
R(2:3)=[1.1,1.2] ANG

leads to the same result as the above two forms.

The type of each element depends on the type of the assigned value, and it is possible to mix types in one variable. Example:

geometry={he}
hf
result=[program,energy,status.gt.0]

yields:

RESULT(1)      =    HF-SCF
RESULT(2)      =        -2.85516048  AU
RESULT(3)      =    TRUE

In this example the variables PROGRAM, ENERGY, and STATUS are system variables, which are set by the program (see section system variables).

As explained already in section setting variables, string variables can be set as other variables in the form

variable =string
variable = string_variable

Strings must be enclosed by quotes. Otherwise the string is assumed to be a variable, and if this is undefined it is assumed to be zero.

Alternatively, if the name of the variable is preceded by a dollar ($), all values are assumed to be a string. This can be a string variable, a quoted string, or an unquoted string. Note that unquoted strings are converted to upper case. Also note that quotes are compulsory if the string contains blanks. Example: $str=[a,b+4,’This is an example for strings’]

yields

STR(1)         =    A
STR(2)         =    B+4
STR(3)         =    This is an example for strings

As a general rule, string variables are replaced by their value only if they are preceded by a dollar ($) (exceptions: in variable definitions, on ''SHOW'' cards, and in logical expressions on ''IF'' cards, the dollar is optional). This is a precaution to avoid commands which have the same name as a variable being interpreted as variables. Variables may also appear on ''TEXT'' or ''TITLE'' cards or in strings, but must be preceded by$ in these cases. Example:

$METHOD=MCSCF R=1.5 TEXT,$method results for R=$R Bohr prints MCSCF results for R=1.5 Bohr String variables can be concatenated with strings or other string variables in the following way. Assume that variable PROGRAM has the value MRCI. Setting METHOD=’$PROGRAM+Q’

sets METHOD to MRCI+Q. Alternatively, if we would also have a variable VERSION with value Q, we could write

METHOD=’$PROGRAM+$VERSION’

Again, the value of METHOD would be MRCI+Q. Note that the quotes are necessary in these cases.

Substring operations are not implemented.

As mentioned above, most system variables cannot be written by the user. In some exceptions, it is possible to redefine them using the SET command:

SET,variable = expression [,] [unit]

This holds for the following variables:

• CHARGE Total charge of the molecule
• NELEC Number of electrons
• SPIN Spin quantum number, given as $2\cdot M\_S$ (integer)
• SCFSPIN Same as SPIN, but only for HF
• MCSPIN Same as SPIN, but only for MCSCF
• CISPIN Same as SPIN, but only for MRCI
• STATE State to be optimized
• MCSTATE Same as STATE but only for MCSCF
• CISTATE Same as STATE but only for MRCI
• SYMMETRY State symmetry
• SCFSYM[METRY] Same as SYMMETRY but only for HF
• MCSYM[METRY] Same as SYMMETRY but only for MCSCF
• CISYM[METRY] Same as SYMMETRY but only for MRCI
• LQUANT Lambda quantum number for linear molecules
• OPTCONV Geometry optimization convergence criterion
• PROGRAM Last program name
• CPUSTEP CPU-time of last program step
• SYSSTEP System-time of last program step
• WALLSTEP Elapsed-time of last program step
• FOCKDONE Indicates if closed-shell fock operator is available.
• MAXBASIS Max number of basis sets stored on dump files. If the maximum is reached, the last one is overwritten when a new one is made, and all information (including dump records etc) of the previous basis is lost. The default is the maximum possible number of basis sets (30), which cannot be exceeded.

String variables for which the stored string has the form of an algebraic expression are evaluated to a number if they are preceded by two dollars ($$). Example: string='a+b' a=3 b=4 text,This is string string which evaluates to$$string

prints

* This is string a+b which evaluates to 7

This can be used to define simple macros, which can be used at various places in the subsequent input. For instance,

ECORR='ENERGY-ESCF' !define a macro
HF                  !do SCF calculation
ESCF=ENERGY         !store SCF energy in variable ESCF
MULTI               !do CASSCF
DEMC=$$ECORR !store CASSCF correlation energy in variable DEMC MRCI !do MRCI DECI=$$ECORR        !store MRCI correlation energy in variable DECI

Here is an example of advanced use of macros and string variables:

examples/oh_macros.inp
***,test for parser
text,This fancy input demonstrates how string variables and macros can be used
text
basis=vdz               !define basis set
geometry={O;H,O,r}      !define geometry (z-matrix)

text,methods
$method=[rhf,2[casscf,2[mrci]]] text,active spaces$spaces=['[3,1,1]',3['[4,2,2]'],3['[5,2,2]']]
text,symmetries
$symset=['1',2['[1,2,3]','1','2']] text,weight factors for state averaged casscf$weights=['1','[1,1,1]',2[' '],'[1,0.5,0.5]',2[' ']]
text,scf occupation
set,scfocc=[3,2[1]]
text,bond distance
r=1.85

hf
do i=1,#method         !loop over methods
mcocc=$$spaces(i) !set active space for this run set,symmetry=$$symset(i)   !set symmetries for this run
set,weight=weights(i)    !set weights for this run
$method(i) !now run method e(i)='$energy'         !save energies in strings
dipol(i)='$dmz' !save dipole moments in strings enddo table,method,spaces,symset,weights,e,dipol title,Results for OH, r=$r, basis=$basis head,method,spaces,symmetries,weights,energies,'dipole moments' exit Variables may be indexed, but only one-dimensional arrays (vectors) are supported. The index may itself be a variable. For instance METHOD(I)=PROGRAM E(I)=ENERGY are valid variable definitions, provided I, PROGRAM, and ENERGY are also defined variables. Indices may be nested to any depth. Different elements of an array can be of different type (either real or logical). However, only one unit can be assigned to an array. String variables have no associated value and cannot be mixed with the other variable types. Therefore, a given variable name can only be used either for a string variable or a real (logical) variable. Vectors (arrays) can be conveniently defined using square brackets: R=[1.0,1.2,1.3] ANG This defines an array with three elements, which can be accessed using indices; for instance, R(2) has the value 1.2 ANG. A repeat specifier can be given in front of the left bracket: 5[0] is equivalent to [0,0,0,0,0]. Brackets can even be nested: for instance, 2[1,2,2[2.1,3.1]] is equivalent to [1,2,2.1,3.1,2.1,3.1,1,2,2.1,3.1,2.1,3.1]. Arrays can be appended from a given position just by entering additional elements; for instance, R(4)=[1.4,1.5] ANG or R(4:)=[1.4,1.5] ANG extends the above array to length 5. Previously defined values can be overwritten. For instance R(2)=[1.25,1.35,1.45] modifies the above vector to (1.0, 1.25, 1.35, 1.45, 1.5). If no index is given on the left hand side of the equal sign, an existing variable of the same name is replaced by the new values, and all old values are lost. For instance • THETA=[100,110,120,130] set four values • THETA(1)=104 replace THETA(1) by a new value; THETA(2:4) are unchanged • THETA=[140,150] old variable THETA is replaced; THETA(3:4) are deleted Square brackets can also be used to define an array of strings, e.g., METHOD=[INT,HF,CASSCF,MRCI] These could be used as follows: DO I=1,4$METHOD(I)
ENDDO

The above input would be equivalent to

INT
HF
CASSCF
MRCI

The current length of an array can be accessed by preceding # to the variable name. For instance, in the above examples #R and #METHOD have the values 5 and 4, respectively. If a variable is not defined, zero is returned but no error occurs. This can be used to test for the existence of a variable, for example:

IF(#SPIN.EQ.0.AND.#NELEC.EQ.1) SET,SPIN=MOD(NELEC,2)

This defines variable SPIN if it is unknown and if NELEC is a scalar (one dimensional) variable.

The following simple vector operations are possible:

• Copying or appending a vector to another vector. For instance S=R copies a vector R to a vector S. S(3)=R copies R to S(3), S(4), …. S(#S+1)=R appends vector R to vector S. It is also possible to access a range of subsequent elements in a vector: S=R(2:4) copies elements 2 to 4 of R to S(1), S(2), S(3). Note that R(2:) denotes elements R(2) to R(#R), but R(2) denotes a single element of R.
• Vector-scalar operations: R=R*2 multiplies each element of R by 2. Instead of the number 2, also scalar (one dimensional) variables or expressions can be used, e.g., R=R*ANG converts all elements of R from Ångstrøm to bohr, or Z=R*COS(THETA) creates a vector Z with elements Z(i) = R(i)*COS(THETA). All other algebraic operators can be used instead of “*”. Note that the scalar must come last since the first variable in the expression determines the vector length.
• Vector-vector operations: If A and B are vectors of the same length, then A \times B is also a vector of this length. Here $\times$ stands for any algebraic operator, and the operation is done for each pair of corresponding elements. For instance, A + B adds the vectors A and B, and A * B multiplies their elements. Note that the latter case is not a scalar product. If an attempt is made to connect two vectors of different lengths by an algebraic operator, an error occurs.
• Intrinsic functions: Assume THETA=[100,110,120,-130] to be a vector of angles (in degrees). In this case X=2*COS(THETA) is also a vector containing the cosines of each element of THETA multiplied by two, i.e., X(i) = 2*COS(THETA(i)). MAX(THETA) or MIN(THETA) return the maximum and minimum values, respectively, in array THETA. Vector operations can also be nested, e.g., MAX(ABS(THETA)) returns the maximum value in array ABS(THETA).

At present, vector operations are not supported with string variables.

A number of variables are predefined by the program. The following variables can be used to convert between atomic units and other units:

EV=1.d0/27.2113839d0 HARTREE
KELVIN=1.d0/3.157747d5 HARTREE
KJOULE=1.d0/2625.500d0 HARTREE
KCAL=1.d0/627.5096d0 HARTREE
CM=1.d0/219474.63067d0 HARTREE
CM-1=1.d0/219474.63067d0 HARTREE
HZ=1.d0/6.5796839207d15 HARTREE
HERTZ=1.d0/6.5796839207d15 HARTREE
ANG=1.d0/0.529177209d0 BOHR
ANGSTROM=1.d0/0.529177209d0 BOHR

TOEV=27.2113839d0 EV
TOK=3.157747d5 K
TOKELVIN=3.157747d5 K
TOCM=219474.63067d0 CM-1
TOHERTZ=6.5796839207d15 HZ
TOHZ=6.5796839207d15 HZ
TOKJ=2625.500d0 KJ/MOL
TOKJOULE=2625.500d0 KJ/MOL
TOKCAL=627.5096d0 KCAL/MOL
TOA=0.529177209d0 ANGSTROM
TOANG=0.529177209d0 ANGSTROM
TODEBYE=2.54158d0 DEBYE

Further variables which are set during execution of the program:

• INTYP defines integral program to be used. Either INTS (Seward) or INTP (Argos).
• INTDONE has the value .true. if the integrals are done for the current geometry.
• CARTESIAN Set to one if Cartesian basis functions are used.
• SCFDONE has the value .true. if an SCF calculation has been done for the current geometry.
• NUMVAR number of variables presently defined
• STATUS status of last step (1=no error, -1=error or no convergence)
• CHARGE Total charge of the molecule
• NELEC number of electrons in last wavefunction
• SPIN spin multiplicity minus one of last wavefunction
• ORBITAL record of last optimized orbitals (set but never used in the program)
• LASTORB Type of last optimized orbitals (RHF, UHF, UHFNAT, or MCSCF).
• LASTSYM Symmetry of wavefunction for last optimized orbitals.
• LASTSPIN $2*M_S$ for wavefunctions for last optimized orbitals.
• LASTNELEC Number of electrons in wavefunction for last optimized orbitals.
• ENERGR(istate) Reference energy for state istate in MRCI and CCSD.
• ENERGY(istate) last computed total energy for state istate for the method specified in the input (e.g., HF, MULTI, CCSD(T), or CCSD[T].
• ENERGY_AVRG State-averaged energy of the MCSCF program multi.
• ENERGY_METHOD String variable holding name of the method used for calculating ENERGY
• ENERGY_BASIS String variable holding name of the orbital basis-set used for calculating ENERGY
• GEOMETRY_METHOD Equal to the value of ENERGY_METHOD for the most recent geometry optimisation
• GEOMETRY_BASIS Equal to the value of ENERGY_BASIS for the most recent geometry optimisation
• ENERGD(istate) Total energy for state istate including Davidson correction (set only in CI).
• ENERGP(istate) Total energy for state istate including Pople correction (set only in CI).
• ENERGT(1) Total energy including perturbative triples (T) correction (set only in CCSD(T), QCI(T)).
• ENERGT(2) Total energy including perturbative triples [T] correction (set only in CCSD(T), QCI(T)).
• ENERGT(3) Total energy including perturbative triples -t correction (set only in CCSD(T), QCI(T)).
• EMP2 holds MP2 energy in MPn, CCSD, BCCD, or QCISD calculations, and RS2 energy in MRPT2 (CASPT2) calculations.
• EMP3 holds MP3 energy in MP3 and MP4 calculations, and RS3 energy in MRPR3 (CASPT3) calculations.
• EMP4 holds MP4(SDQ) energy in MP4 calculations. The MP4(SDTQ) energy is stored in variable ENERGY.
• METHODC String variable holding name of the methods used for ENERGC, e.g., CCSD, BCCD, QCI.
• METHODT(1) String variable holding name of the methods used for ENERGT(1), e.g., CCSD(T), BCCD(T), QCI(T).
• METHODT(2) String variable holding name of the methods used for ENERGT(2), e.g., CCSD[T], BCCD[T], QCI[T].
• METHODT(3) String variable holding name of the methods used for ENERGT(3), e.g., CCSD-T, BCCD-T, QCI-T.
• ENERGC Total energy excluding perturbative triples correction (set only in QCI or CCSD with triples correction enabled).
• DFTFUN total value of density functional in DFT or KS.
• DFTFUNS(ifun) value of ifun’th component of density functional in DFT or KS.
• DFTNAME(ifun) name of ifun’th component of density functional in DFT or KS.
• DFTFAC(ifun) factor multiplying ifun’th component of density functional in DFT or KS.
• DFTEXFAC factor multiplying exact exchange in KS.
• PROP(istate) computed property for state istate. See below for the names PROP of various properties.
• PROGRAM last program called, as specified in the input (e.g., HF, CCSD(T), etc.)
• ITERATIONS Number of iterations used. Set negative if no convergence or max number of iterations reached.
• CPUSTEP User-CPU time in seconds for last program called.
• SYSSTEP System-CPU time in seconds for last program called.
• WALLSTEP Elapsed time in seconds for last program called.

The variable names for properties are the same as used on the EXPEC input cards.

• OV Overlap
• EKIN Kinetic energy
• POT Potential
• DELTA Delta function
• DEL4 $\nabla^4$
• DARWIN Darwin term of relativistic correction
• MASSV Mass-velocity term of relativistic correction
• EREL Total relativistic correction
• DMX, DMY, DMZ Dipole moments
• XX, YY, ZZ, XY, XZ, XY Second moments
• XXX, XXY, XXZ, XYY, XYZ, XZZ, YYY, YYZ, YZZ, ZZZ Third moments
• QMXX, QMYY, QMZZ, QMXY, QMXZ, QMXY Quadrupole moments
• EFX, EFY, EFZ Electric field
• FGXX, FGYY, FGZZ, FGXY, FGXZ, FGXY Electric field gradients
• D/DX, D/DY, D/DZ Velocity
• LSX, LSY, LSZ One-electron spin-orbit
• LL Total angular momentum squared $L^2$
• LX, LY, LZ Electronic angular momentum
• LXLX, LYLY, LZLZ, LXLY, LXLZ, LYLZ Two-electron angular momentum

By default, only the dipole moments are computed and defined. The values of other properties are only stored in variables if they are requested by EXPEC cards. If more than one state is computed (e.g., in state-averaged MCSCF, corresponding arrays PROP(istate) are returned. If properties are computed for more than one center, the center number is appended to the name, e.g. EFX1, EFX2 etc.

If transition properties are computed, their values are stored in corresponding variables with prefix TR, e.g., TRDMX, TRDMY, TRDMZ for transition dipole moments. If more than two states are computed, the index is $(i-1)*(i-2)/2+j$, where $i \gt j \ge 1$ are state numbers. In a state-averaged calculation, states are counted sequentially for all state symmetries.

For instance, in the following state-averaged MCSCF

MULTI;WF,14,1,0;STATE,3;WF,14,2,0;STATE,2;WF,14,3,0

the states are counted as

 $i$ 1 2 3 4 5 6 Symmetry 1 1 1 2 2 3 Root in Sym. 1 2 3 1 2 1

All variables described below are checked by the program, but not set (except NELEC and SPIN). If these are not defined by the user, the program uses its internal defaults. The variables are only recognized and used if defined using the SET command, e.g.

SET,MCOCC=[6,3,2]
SET,STATE=2

etc.

Variables recognized by the SCF program:

• CHARGE Total charge of the molecule (can be given instead of nelec)
• NELEC number of electrons
• SPIN spin multiplicity minus one
• SCFSYM[METRY] wavefunction symmetry
• SYMMETRY as SCFSYMM; only used if SCFSYMM is not present.
• SCFOC[C] number of occupied orbitals in each symmetry for SCF
• SCFCL[OSED] number of closed-shell orbitals in each symmetry for SCF
• SCFORB record of saved orbitals in SCF
• SCFSTART record of starting orbitals used in SCF

Variables recognized by the MCSCF program:

• CHARGE Total charge of the molecule (can be given instead of nelec)
• NELEC number of electrons
• MCSYM[METRY] wavefunction symmetry. This can be an array for state-averaged calculations.
• SYMMETRY as MCSYMM; only used if MCSYMM is not present.
• MCSPIN spin multiplicity minus one. This can be an array for state-averaged calculations, but different spin multiplicities can only be used in determinant CASSCF. If only one value is specified, this is used for all states
• SPIN as MCSPIN; only used if MCSPIN is not present.
• MCSTATE number of states for each symmetry in MCSCF
• STATE as MCSTATE; only used if MCSTATE is not present.
• WEIGHT weight factors for all states defined by SYMMETRY and STATE
• LQUANT Eigenvalues of $L_z^2$ for linear molecules for each state defined by SYMMETRY and STATE.
• MCSELECT records from which configurations can be selected and selection threshold
• SELECT as MCSELECT; only used if MCSELECT is not present.
• MCRESTRICT can be used to define occupancy restrictions
• RESTRICT as MCRESTRCT; only used if MCRESTRICT is not present:
• CONFIG if set to .true. or to one triggers use of CSFs
• MCOC[C] number of occupied orbitals in each symmetry
• OCC as MCOCC; only used if MCOCC is not present.
• MCCL[OSED] number of optimized closed-shell orbitals in each symmetry
• CLOSED as MCCLOSED; only used if MCCLOSED is not present.
• MCFROZEN number of frozen core orbitals in each symmetry
• FROZEN as MCFROZEN; only used if MCFROZEN is not present.
• MCSTART record of starting orbitals
• COREORB record of frozen core orbitals
• MCORB record for saving optimized orbitals
• MCSAVE records for saving CI wavefunction (like SAVE card in MCSCF)

Variables recognized by the CI/CCSD program:

• CHARGE Total charge of the molecule (can be given instead of nelec)
• NELEC number of electrons
• SPIN spin multiplicity minus one
• CISYM[METRY] wavefunction symmetry. If this is an array, only SYMMETRY(1) is used.
• SYMMETRY as CISYMM; only used if CISYMM is not present.
• CISTATE number of states in CI
• STATE as CISTATE, only used if CISTATE is not present.
• CISELECT records from which configurations can be selected
• SELECT as CISELECT; only used if CISELCT is not present.
• CIRESTRICT defines occupancy restrictions
• RESTRICT as RESTRICT; only used if CIRESTRICT is not present.
• CIOC[C] number of occupied orbitals in each symmetry
• OCC as CIOCC; only used if CIOCC is not present.
• CICL[OSED] number of closed-shell orbitals in each symmetry
• CLOSED as CICLOSED; only used if CICLOSED is not present.
• CICO[RE] number of core orbitals in each symmetry
• CORE as CICORE; only used if CICORE is not present.
• CIORB record of orbitals used in CI
• CISAVE records for saving CI wavefunction (like SAVE card in CI)
• CISTART records for restarting with previous CI wavefunction (like START card in CI)

Variables recognized by the DFT/KS program:

• DF(ifun) or DFTNAME(ifun) name of ifun’th component of density functional.
• DFTFAC(ifun) factor multiplying ifun’th component of density functional.
• DFTEXFAC factor multiplying exact exchange in KS.

Example for the use of these variables for a state-averaged MCSCF (note that system variables can only be modified using the SET command, see section system variables):

• SET,NELEC=9 defines number of electrons
• SET,SPIN=1 defines wavefunction to be a doublet
• SET,SYMMETRY=[1,2,3] defines wavefunction symmetries for state averaged calculation
• SET,STATE=[2,1,1] defines number of states to be averaged in each symmetry
• WEIGHT=[2,2,1,1] defines weights for the above four states
• OCC=[5,2,2] number of occupied orbitals in each symmetry
• CLOSED=2 number of closed-shell orbitals in symmetry 1
• MCORB=3100.2 record for optimized orbitals
• MULTI do mcscf with above parameters

Note: Setting the variables NELEC, SPIN, or SYMMETRY, has the same effect giving these on a gobal WF directive. If the global WF directive is given after the variable definition, the values of the variables are replaced by the values given on the WF directive. Vice versa, if a variable definition follows a gobal WF directive, the new value of the variable is used in the following. Note that WF input cards in command blocks have preference over global WF directives or input variables.

Variables or the results of expressions can be displayed in the output using SHOW and TABLE.

The general form of the SHOW command is as follows:

SHOW[ncol,format],expression

where expression can be an expression or variable, ncol is the number of values printed per line (default 6), and format is a format (default 6F15.8). This can be used to print vectors in matrix form. The specification of ncol and format is optional. Assume that E is a vector:

• SHOW,E prints E using defaults.
• SHOW[n],E prints E with n elements per line; (if n>6, more than one line is needed, but in any case a new line is started after n elements).
• SHOW[n,10f10.4],E prints E in the format given, with newline forced after n elements.

Note that the total length of the format should not exceed 100 characters (a left margin of 30 characters is always needed).

A wild card format can be used to show several variables more easily:

SHOW,qm*,dm*

shows all variables whose names begin with QM and DM. Note that no letters must appear after the , i.e., the wild card format is less general than in UNIX commands.

See the TABLE command for another possibility to tabulate results.

Variables can be deleted using

CLEAR,name1, name2, …

Wild cards can be used as in SHOW, e.g.,

CLEAR,ENERG*

clears all variables whose names begin with ENERG. All variables can be cleared using

CLEARALL

The length of vectors can be truncated simply by redefining the length specifier: #R=2 truncates the array R to length 2. Higher elements are no longer available (but could be redefined). Setting #R=0 is equivalent to the command CLEAR,R.

Variables can be read from an external file using

READVAR, filename, [option]

Such files can be saved, for instance by the geometry optimization program, and reused later to recover a certain optimized geometry. The format of the input in filename is the same as for ordinary input.

If option=NOINDEX|IGNOREINDEX is given then variable indices are ignored and only the last value saved is read (without index). This can be useful if for example a file saved with SAVEACT in a geometry optimization is read, and it is intended to continue with the variables that were saved last.