Combined Quantum and Molecular Mechanical Hamiltonian
A combined quantum (QM) and molecular (MM) mechanical potential
allows for the study of condensed phase chemical reactions, reactive
intermediates, and excited state isomerizations. This is necessary
since standard MM force fields are parameterized with experimental
data on the potential energy surface which may be far removed from
the region of interest, or have the wrong analytical
form. A full decription of the theory and application is given in
J. Computational Chemistry (1990) 6, 700.
The effective Hamiltonian, Heff, describes the energy and forces on
each atom. It is treated as a sum of four terms, Hqm, Hmm, Hqm/mm,
and Hbrdy.
Hqm Describes the quantum mechanical particles. The two semi-
empirical methods available are AM1 and MNDO. Both treat
hydrogen, first row elements plus silicon, phosphorus,
sulfur, and the halogens. MNDO has additional parameters
for aluminium, phosphorus, chromium, germanium, tin, mercury,
and lead. Full details concerning these theoretical methods
can be found in Dewar's original papers, JACS (1985) 107,
3902, JACS (1977) 99, 4899, Theoret. Chim. Acta. (1977) 46, 89.
Hmm The molecular mechanical Hamiltonian is independent of the
coordinates of the electrons and nuclei of the QM atoms.
CHARMM22 is used to treat atoms in this region.
Hqm/mm The combined Hamiltonian describes how QM and MM atoms
interact. This is composed of two electrostatic and one
van der Waals terms. Each MM atom interacts with both the
electrons and nuclei of the QM atoms (therefore two terms).
The van der Waals term is necessary since some MM atoms
possess no charge and would consequently be invisible to
the QM atoms, and in other cases often provide the only
difference in the interaction (Cl vs. Br).
Hbrdy The usual periodic or stochastic boundary conditions are
implemented.
The quantum mechanical package MOPAC 4.0 was interfaced with
CHARMM22. This was provided by James P. P. Stewart from the Air Force
Academy. There are several limitations with the current program
implemntation. The current plan is to update the quantum mechanical
procedures to MOPAC 6.0, to include vibrational analysis using
analytical functions, with the possibility of using free energy
perturbation.
* Menu:
* Syntax:: Syntax of QM/MM Commands
* Description:: Brief Description of Quantum Commands
Syntax for QUANTUM commands
QUANtum [atom-selection]
[IFIL int] [ITRMax int]
[CAMP] [KING] [PULAy]
[SHIFt real] [SCFCriteria real]
[UHF] [C.I.] [EXCIted] [NMOS int] [MICR int]
[TRIPLET|QUARTET|QUINTET|SEXTET]
[AM1|MNDO] [CHARge int]
[ALPM real] [RHO0 real] [SFT1 real]
[EXCIted] [BIRADical] [C.I.]
[ITER] [EIG2] [ENERGY] [ PL ]
[DEBUG [1ELEC] [DENSITY] [FOCK] [VECTor]]
MULLiken
ADDLinkatom link-atom-name atom-spec atom-spec
RELLinkatom link-atom-name atom-spec atom-spec
link-atom-name ::= a four character descriptor starting with QQ.
atom-spec::= {residue-number atom-name}
{ segid resid atom-name }
{ BYNUm atom-number }
Description of QUANtum Commands
Most keywords preceed an equal sign followed by an appropriate
value. A description of each is given below.
1ELECtron The final one-electron matrix is printed out. This matrix
is composed of atomic orbitals; the array element between
orbitals i and j on different atoms is given by,
H(i,j) = 0.5 (beta(i) + beta(j)(overlap(i,j))
The matrix elements between orbitals i and j on the same
atom are calculated from the electron-nuclear attraction
energy, and also from the U(i) value if i=j.
The one-electron matrix is unaffected by (a) the charge and
(b) the electron density. It is only a function of the
geometry. Abbreviation: 1ELEC.
0SCF The data can be read in and output, but no actual
calculation is performed when this keyword is used.
This is useful as a check on the input data.
All obvious errors are trapped, and warning messages printed.
A second use is to convert from one format to another.
The input geometry is printed in various formats at the
end of a 0SCF calculation. If NOINTER is absent, cartesian
coordinates are printed.
Unconditionally, MOPAC Z-matrix internal coordinates are
printed, and if AIGOUT is present, Gaussian Z-matrix
internal coordinates are printed. 0SCF should now be used
in place of DDUM.
1SCF When users want to examine the results of a single SCF
calculation of a geometry, 1SCF should be used. 1SCF can
be used in conjunction with RESTART, in which case a single
SCF calculation will be done, and the results printed.
When 1SCF is used on its own (that is, RESTART is not also
used) then derivatives will only be calculated if GRAD is
also specified. 1SCF is helpful in a learning situation.
MOPAC normally performs many SCF calculations, and in
order to minimize output when following the working of the
SCF calculation, 1SCF is very useful.
AM1 The AM1 method is to be used. By default MNDO is run.
ANALYTical By default, finite difference derivatives of energy with
respect to geometry are used. If ANALYT is specified,
then analytical derivatives are used instead. Since the
analytical derivatives are over Gaussian functions --
a STO-6G basis set is used -- the overlaps are also over
Gaussian functions. This will result in a very small
(less than 0.1 Kcal/mole) change in heat of formation.
Use analytical derivatives (a) when the mantissa used is
less than about 51-53 bits, or (b) when comparison with
finite difference is desired. Finite difference
derivatives are still used when non-variationally optimized
wavefunctions are present.
BIRADical NOTE: BIRADICAL is a redundant keyword, and represents a
particular configuration interaction calculation.
Experienced users of MECI (q.v.) can duplicate the effect
of the keyword BIRADICAL by using the MECI keywords
OPEN(2,2) and SINGLET. For molecules which are believed to
have biradicaloid character the option exists to optimize
the lowest singlet energy state which results from the
mixing of three states. These states are, in order, (1) the
(micro)state arising from a one electron excitation from
the HOMO to the LUMO, which is combined with the microstate
resulting from the time-reversal operator acting on the
parent microstate, the result being a full singlet state;
(2) the state resulting from de-excitation from the formal
LUMO to the HOMO; and (3) the state resulting from the single
electron in the formal HOMO being excited into the LUMO.
Microstate 1 Microstate 2 Microstate 3
Alpha Beta Alpha Beta Alpha Beta Alpha Beta
LUMO * * * *
--- --- --- --- --- --- --- ---
+
HOMO * * * *
--- --- --- --- --- --- --- ---
A configuration interaction calculation is involved here.
A biradical calculation done without C.I. at the RHF
level would be meaningless. Either rotational invariance
would be lost, as in the D2d form of ethylene, or very
artificial barriers to rotations would be found, such as in
a methane molecule "orbiting" a D2d ethylene. In both
cases the inclusion of limited configuration interaction
corrects the error. BIRADICAL should not be used if
either the HOMO or LUMO is degenerate; in
this case, the full manifold of HOMO x LUMO should be
included in the C.I., using MECI options. The user should
be aware of this situation. When the biradical
calculation is performed correctly, the result is normally
a net stabilization. However, if the first singlet
excited state is much higher in energy than the
closed-shell ground state, BIRADICAL can lead to a
destabilization. Abbreviation: BIRAD. See also MECI,
C.I., OPEN, SINGLET.
CAMKINg
CHARge When the system being studied is an ion, the charge, n, on
the ion must be supplied by CHARGE=n. For cations n can be
1 or 2 or 3, etc, for anions -1 or -2 or -3, etc.
EXAMPLES
ION KEYWORD ION KEYWORD
NH4(+) CHARGE=1 CH3COO(-) CHARGE=-1
C2H5(+) CHARGE=1 (COO)(=) CHARGE=-2
SO4(=) CHARGE=-2 PO4(3-) CHARGE=-3
HSO4(-) CHARGE=-1 H2PO4(-) CHARGE=-1
C.I. Normally configuration interaction is invoked if any of the
keywords which imply a C.I. calculation are used, such as
BIRADICAL, TRIPLET or QUARTET. Note that ROOT= does not
imply a C.I. calculation: ROOT= is only used when a C.I.
calculation is done. However, as these implied C.I.'s
involve the minimum number of configurations practical,
the user may want to define a larger than minimum C.I., in
which case the keyword C.I.=n can be used. When C.I.=n is
specified, the n M.O.'s which "bracket" the occupied-
virtual energy levels will be used. Thus, C.I.=2 will
include both the HOMO and the LUMO, while C.I.=1 (implied
for odd-electron systems) will only include the HOMO
(This will do nothing for a closed-shell system, and leads
to Dewar's half-electron correction for odd-electron
systems). Users should be aware of the rapid increase
in the size of the C.I. with increasing numbers of M.O.'s
being used. Numbers of microstates implied by the use of
the keyword C.I.=n on its own are as follows:
Keyword Even-electron systems Odd-electron systems
No. of electrons, configs No. of electrons, configs
Alpha Beta Alpha Beta
C.I.=1 1 1 1 1 0 1
C.I.=2 1 1 4 1 0 2
C.I.=3 2 2 9 2 1 9
C.I.=4 2 2 36 2 1 24
C.I.=5 3 3 100 3 2 100
C.I.=6 3 3 400 3 2 300
C.I.=7 4 4 1225 4 3 1225
C.I.=8 (Do not use unless other keywords also used, see below)
If a change of spin is defined, then larger numbers of
M.O.'s can be used up to a maximum of 10. The C.I. matrix
is of size 100 x 100. For calculations involving up to 100
configurations, the spin-states are exact eigenstates of
the spin operators. For systems with more than 100
configurations, the 100 configurations of lowest energy are
used. See also MICROS and the keywords defining spin-states.
Note that for any system, use of C.I.=5 or higher normally
implies the diagonalization of a 100 by 100 matrix. As a
geometry optimization using a C.I. requires the derivatives
to be calculated using derivatives of the C.I. matrix,
geometry optimization with large C.I.'s will require more
time than smaller C.I.'s.
Associated keywords: MECI, ROOT=, MICROS, SINGLET, DOUBLET, etc.
C.I.=(n,m) In addition to specifying the number of M.O.'s in the
active space, the number of electrons can also be defined.
In C.I.=(n,m), n is the number of M.O.s in the active
space, and m is the number of doubly filled levels to be used.
EXAMPLES
Keywords Number of M.O.s No. Electrons
C.I.=2 2 2 (1)
C.I.=(2,1) 2 2 (3)
C.I.=(3,1) 3 2 (3)
C.I.=(3,2) 3 4 (5)
C.I.=(3,0) OPEN(2,3) 3 2 (N/A)
C.I.=(3,1) OPEN(2,2) 3 4 (N/A)
C.I.=(3,1) OPEN(1,2) 3 N/A (3)
Odd electron systems given in parentheses.
DEBUG Certain keywords have specific output control meanings, such as
FOCK, VECTORS and DENSITY. If they are used, only the final
arrays of the relevant type are printed. If DEBUG is supplied,
then all arrays are printed. This is useful in debugging
ITER. DEBUG can also increase the amount of output produced
when certain output keywords are used, e.g. COMPFG.
DCART The cartesian derivatives which are calculated in DCART for
variationally optimized systems are printed if the keyword
DCART is present. The derivatives are in units of
kcals/Angstrom, and the coordinates are displacements
in x, y, and z.
DENSITY At the end of a job, when the results are being printed,
the density matrix is also printed. For RHF the normal
density matrix is printed. For UHF the sum of the alpha
and beta density matrices is printed.
If density is not requested, then the diagonal of the
density matrix, i.e., the electron density on the atomic
orbitals, will be printed.
DOUBLet When a configuration interaction calculation is done,
all spin states are calculated simultaneously, either
for component of spin = 0 or 1/2. When only doublet states
are of interest, then DOUBLET can be specified, and all
other spin states, while calculated, are ignored in the
choice of root to be used.
Note that while almost every odd-electron system will have
a doublet ground state, DOUBLET should still be specified
if the desired state must be a doublet.
DOUBLET has no meaning in a UHF calculation.
EIGS
EIG2
ENERGY
ESR The unpaired spin density arising from an odd-electron
system can be calculated both RHF and UHF. In a UHF
calculation the alpha and beta M.O.'s have different
spatial forms, so unpaired spin density can naturally
be present on in-plane hydrogen atoms such as in the phenoxy
radical.
In the RHF formalism a MECI calculation is performed. If the
keywords OPEN and C.I.= are both absent then only a single
state is calculated. The unpaired spin density is then
calculated from the state function. In order to have
unpaired spin density on the hydrogens in, for example,
the phenoxy radical, several states should be mixed.
EXCIted The state to be calculated is the first excited open-shell
singlet state. If the ground state is a singlet, then the
state calculated will be S(1); if the ground state is a
triplet, then S(2). This state would normally be the
state resulting from a one-electron excitation from the
HOMO to the LUMO. Exceptions would be if the lowest
singlet state were a biradical, in which case the EXCITED
state could be a closed shell.
The EXCITED state will be calculated from a BIRADICAL
calculation in which the second root of the C.I. matrix is
selected. Note that the eigenvector of the C.I. matrix is
not used in the current formalism.
Abbreviation: EXCI.
NOTE: EXCITED is a redundant keyword, and represents a
particular configuration interaction calculation.
Experienced users of MECI can duplicate the effect of the
keyword EXCITED by using the MECI keywords OPEN(2,2),
SINGLET, and ROOT=2.
FOCK
FORCE A force-calculation is to be run. The Hessian, that is
the matrix (in millidynes per Angstrom) of second
derivatives of the energy with respect to displacements of
all pairs of atoms in x, y, and z directions, is
calculated. On diagonalization this gives the force
constants for the molecule. The force matrix, weighted
for isotopic masses, is then used for calculating the
vibrational frequencies. The system can be characterized
as a ground state or a transition state by the presence of
five (for a linear system) or six eigenvalues which are
very small (less than about 30 reciprocal centimeters). A
transition state is further characterized by one, and
exactly one, negative force constant.
A FORCE calculation is a prerequisite for a THERMO calculation.
Before a FORCE calculation is started, a check is made to
ensure that a stationary point is being used. This check
involves calculating the gradient norm (GNORM) and if it is
significant, the GNORM will be reduced using BFGS.
All internal coordinates are optimized, and any symmetry
constraints are ignored at this point. An implication of
this is that if the specification of the geometry relies on
any angles being exactly 180 or zero degrees, the
calculation may fail.
The geometric definition supplied to FORCE should not rely
on angles or dihedrals assuming exact values. (The test
of exact linearity is sufficiently slack that most
molecules that are linear, such as acetylene and but-2-yne,
should not be stopped.) See also THERMO, LET, TRANS,
ISOTOPE.
In a FORCE calculation, PRECISE will eliminate quartic
contamination (part of the anharmonicity). This is
normally not important, therefore PRECISE should not
routinely be used.
In a FORCE calculation, the SCF criterion is automatically
made more stringent; this is the main cause of the SCF
failing in a FORCE calculation.
ITER The default maximum number of SCF iterations is 200.
When this limit presents difficulty, ITRY=nn can be used
to re-define it. For example, if ITRY=400 is used, the
maximum number of iterations will be set to 400. ITRY
should normally not be changed until all other means of
obtaining a SCF have been exhausted, e.g. PULAY CAMP-KING etc.
INTERP
LPULAY
LARGE Most of the time the output invoked by keywords is
sufficient. LARGE will cause less-commonly wanted, but
still useful, output to be printed.
1. To save space, DRC and IRC outputs will, by default,
only print the line with the percent sign. Other output
can be obtained by use of the keyword LARGE, according to
the following rules:
Keyword Effect
LARGE Print all internal and cartesian coordinates
and cartesian velocities.
LARGE=1 Print all internal coordinates.
LARGE=-1 Print all internal and cartesian coordinates
and cartesian velocities.
LARGE=n Print every n'th set of internal coordinates.
LARGE=-n Print every n'th set of internal and cartesian
coordinates and cartesian velocities.
If LARGE=1 is used, the output will be the same as that of
Version 5.0, when LARGE was not used. If LARGE is used, the
output will be the same as that of Version 5.0, when LARGE
was used. To save disk space, do not use LARGE.
MECI At the end of the calculation details of the Multi Electron
Configuration Interaction calculation are printed if MECI
is specified. The state vectors can be printed by
specifying VECTORS. The MECI calculation is either
invoked automatically, or explicitly invoked by the use of
the C.I.=n keyword.
MICRos The microstates used by MECI are normally generated by use
of a permutation operator. When individually defined
microstates are desired, then MICROS=n can be used, where
n defines the number of microstates to be read in.
Format for Microstates
After the geometry data plus any symmetry data are read in,
data defining each microstate is read in, using format
20I1, one microstate per line. The microstate data is
preceded by the word "MICROS" on a line by itself. There
is at present no mechanism for using MICROS with a reaction path.
For a system with n M.O.'s in the C.I. (use OPEN=(n1,n) or
C.I.=n to do this), the populations of the n alpha M.O.'s
are defined, followed by the n beta M.O.'s. Allowed
occupancies are zero and one. For n=6 the closed-shell
ground state would be defined as 111000111000, meaning one
electron in each of the first three alpha M.O.'s, and one
electron in each of the first three beta M.O.'s.
Users are warned that they are responsible for completing
any spin manifolds. Thus while the state 111100110000
is a triplet state with component of spin = 1, the state
111000110100, while having a component of spin = 0 is
neither a singlet nor a triplet. In order to complete the
spin manifold the microstate 110100111000 must also be included.
If a manifold of spin states is not complete, then the
eigenstates of the spin operator will not be quantized.
When and only when 100 or fewer microstates are supplied,
can spin quantization be conserved.
There are two other limitations on possible microstates.
First, the number of electrons in every microstate should
be the same. If they differ, a warning message will be
printed, and the calculation continued (but the results
will almost certainly be nonsense). Second, the component
of spin for every microstate must be the same, except for
teaching purposes. Two microstates of different
components of spin will have a zero matrix element
connecting them. No warning will be given as this is a
reasonable operation in a teaching situation. For example, if
all states arising from two electrons in two levels are to
be calculated say for teaching Russel-Saunders coupling,
then the following microstates would be used:
Microstate No. of alpha, beta electrons Ms State
1100 2 0 1 Triplet
1010 1 1 0 Singlet
1001 1 1 0 Mixed
0110 1 1 0 Mixed
0101 1 1 0 Singlet
0011 0 2 -1 Triplet
Constraints on the space manifold are just as rigorous, but
much easier to satisfy. If the energy levels are
degenerate, then all components of a manifold of degenerate
M.O.'s should be either included or excluded. If only
some, but not all, components are used, the required
degeneracy of the states will be missing.
As an example, for the tetrahedral methane cation, if the user
supplies the microstates corresponding to a component of
spin = 3/2, neglecting Jahn-Teller distortion, the minimum
number of states that can be supplied is 90 = (6!/(1!*5!))*
(6!/(4!*2!)).
While the total number of electrons should be the same for all
microstates, this number does not need to be the same as
the number of electrons supplied to the C.I.; thus in the
example above, a cationic state could be 110000111000.
The format is defined as 20I1 so that spaces can be used
for empty M.O.'s.
MNDO The default Hamiltonian within MOPAC is MNDO, with the
alternatives of AM1 and MINDO/3. To use the MINDO/3
Hamiltonian the keyword MINDO/3 should be used. Acceptable
alternatives to the keyword MINDO/3 are MINDO and MINDO3.
PRECISE The criteria for terminating all optimizations, electronic and
geometric, are to be increased by a factor, normally, 100.
This can be used where more precise results are wanted. If
the results are going to be used in a FORCE calculation,
where the geometry needs to be known quite precisely, then
PRECISE is recommended; for small systems the extra cost in
CPU time is minimal.
PRECISE is not recommended for experienced users, instead
GNORM=n.nn and SCFCRT=n.nn are suggested. PRECISE should
only very rarely be necessary in a FORCE calculation: all
it does is remove quartic contamination, which only affects
the trivial modes significantly, and is very expensive
in CPU time.
PULAy The default converger in the SCF calculation is to be
replaced by Pulay's procedure as soon as the density matrix
is sufficiently stable. A considerable improvement in
speed can be achieved by the use of PULAY. If a large
number of SCF calculations are envisaged, a sample calculation
using 1SCF and PULAY should be compared with using 1SCF on
its own, and if a saving in time results, then PULAY should
be used in the full calculation. PULAY should be used with
care in that its use will prevent the combined package of
convergers (SHIFT, PULAY and the CAMP-KING convergers)
from automatically being used in the event that the system
fails to go SCF in (ITRY-10) iterations.
The combined set of convergers very seldom fails.
QUARTet RHF interpretation: The desired spin-state is a quartet,
i.e., the state with component of spin = 1/2 and spin =
3/2. When a configuration interaction calculation is done,
all spin states of spin equal to, or greater than 1/2 are
calculated simultaneously, for component of spin = 1/2.
From these states the quartet states are selected when
QUARTET is specified, and all other spin states, while
calculated, are ignored in the choice of root to be used.
If QUARTET is used on its own, then a single state,
corresponding to an alpha electron in each of three M.O.'s
is calculated.
UHF interpretation: The system will have three more alpha
electrons than beta electrons.
QUINTet RHF interpretation: The desired spin-state is a quintet,
that is, the state with component of spin = 0 and spin = 2.
When a configuration interaction calculation is done, all
spin states of spin equal to, or greater than 0 are
calculated simultaneously, for component of spin = 0.
From these states the quintet states are selected when
QUINTET is specified, and the septet states, while
calculated, will be ignored in the choice of root to be
used. If QUINTET is used on its own, then a single state,
corresponding to an alpha electron in each of four M.O.'s
is calculated.
UHF interpretation: The system will have three more alpha
electrons than beta electrons.
ROOT The n'th root of a C.I. calculation is to be used in the
calculation. If a keyword specifying the spin-state is
also present, e.g. SINGLET or TRIPLET, then the n'th root
of that state will be selected. Thus ROOT=3 and SINGLET
will select the third singlet root. If ROOT=3 is used on
its own, then the third root will be used, which may be a
triplet, the third singlet, or the second singlet (the
second root might be a triplet). In normal use, this
keyword would not be used. It is retained for educational
and research purposes. Unusual care should be exercised
when ROOT= is specified.
SCFCrt The default SCF criterion is to be replaced by that defined
by SCFCRT=. The SCF criterion is the change in energy in
kcal/mol on two successive iterations. Other minor
criteria may make the requirements for an SCF slightly more
stringent. The SCF criterion can be varied from about
0.001 to 1.D-25, although numbers in the range 0.0001 to
1.D-9 will suffice for most applications.
An overly tight criterion can lead to failure to achieve a
SCF, and consequent failure of the run.
SEXTet RHF interpretation: The desired spin-state is a sextet:
the state with component of spin = 1/2 and spin = 5/2.
The sextet states are the highest spin states normally
calculable using MOPAC in its unmodified form. If SEXTET
is used on its own, then a single state, corresponding to
one alpha electron in each of five M.O.'s, is calculated.
If several sextets are to be calculated, say the second
or third, then OPEN(n1,n2) should be used.
UHF interpretation: The system will have five more alpha
electrons than beta electrons.
SHIFt In an attempt to obtain an SCF by damping oscillations
which slow down the convergence or prevent an SCF being
achieved, the virtual M.O. energy levels are shifted up or
down in energy by a shift technique. The principle is that
if the virtual M.O.'s are changed in energy relative to
the occupied set, then the polarizability of the occupied
M.O.'s will change pro rata. Normally, oscillations are
due to autoregenerative charge fluctuations.
The SHIFT method has been re-written so that the value of
SHIFT changes automatically to give a critically-damped
system. This can result in a positive or negative shift
of the virtual M.O. energy levels. If a non-zero SHIFT
is specified, it will be used to start the SHIFT technique,
rather than the default 15eV. If SHIFT=0 is specified,
the SHIFT technique will not be used unless normal
convergence techniques fail and the automatic "ALL
CONVERGERS..." message is produced.
SINGLet When a configuration interaction calculation is done, all spin
states are calculated simultaneously, either for component
of spin = 0 or 1/2. When only singlet states are of
interest, then SINGLET can be specified, and all other spin
states, while calculated, are ignored in the choice of root
to be used.
Note that while almost every even-electron system will
have a singlet ground state, SINGLET should still be
specified if the desired state must be a singlet.
SINGLET has no meaning in a UHF calculation, but see also TRIPLET.
TRIPLet The triplet state is defined. If the system has an odd
number of electrons, an error message will be printed.
UHF interpretation. The number of alpha electrons exceeds
that of the beta electrons by 2. If TRIPLET is not
specified, then the numbers of alpha and beta electrons are
set equal. This does not necessarily correspond to a singlet.
RHF interpretation.
An RHF MECI calculation is performed to calculate the
triplet state. If no other C.I. keywords are used, then
only one state is calculated by default. The occupancy of
the M.O.'s in the SCF calculation is defined as
(...2,1,1,0,..), that is, one electron is put in each of
the two highest occupied M.O.'s.
See keywords C.I.=n and OPEN(n1,n2).
UHF The unrestricted Hartree-Fock Hamiltonian is to be used.
VECTors The eigenvectors are to be printed. In UHF calculations
both alpha and beta eigenvectors are printed; in all cases
the full set, occupied and virtual, are output. The
eigenvectors are normalized to unity, that is the sum of
the squares of the coefficients is exactly one. If DEBUG
is specified, then ALL eigenvectors on every iteration of
every SCF calculation will be printed. This is useful in
a learning context, but would normally be very undesirable.
NIH/DCRT/Laboratory for Structural Biology
FDA/CBER/OVRR Biophysics Laboratory