For an ADC calculation it is important to ensure that there are sufficient resources
available for the necessary integral calculations and transformations. These resources
are controlled using the *$rem* variables MEM_STATIC and MEM_TOTAL.
The memory used by ADC is currently 95% of the difference
MEM_TOTAL - MEM_STATIC.

An ADC calculation is requested by setting the *$rem* variable METHOD to the
respective ADC variant. Furthermore, the number of excited states to be calculated
has to be specified using one of the *$rem* variables EE_STATES,
EE_SINGLETS, or EE_TRIPLETS. The former variable should be used for
open-shell or unrestricted closed-shell calculations, while the latter two variables are
intended for restricted closed-shell calculations. Even though not recommended, it is
possible to use EE_STATES in a restricted calculation which translates into
EE_SINGLETS, if neither EE_SINGLETS nor EE_TRIPLETS is set.
Similarly, the use EE_SINGLETS in an unrestricted calculation will translate
into EE_STATES, if the latter is not set as well.

All *$rem* variables to set the number of excited states accept either an integer number
or a vector of integer numbers. A single number specifies that the same number of excited
states are calculated for every irreducible representation the point group of the
molecular system possesses (molecules without symmetry are treated as ${C}_{1}$ symmetric).
In contrast, a vector of numbers determines the number of states for each irreducible
representation explicitly. Thus, the length of the vector always has to match the number
of irreducible representations. Hereby, the excited states are labeled according to the
irreducible representation of the electronic transition which might be different from
the irreducible representation of the excited state wave function.
Users can choose to calculate any molecule as ${C}_{1}$ symmetric by setting
CC_SYMMETRY = FALSE.

METHOD

Controls the order in perturbation theory of ADC.

TYPE:

STRING

DEFAULT:

None

OPTIONS:

ADC(1)
Perform ADC(1) calculation.
ADC(2)
Perform ADC(2)-s calculation.
ADC(2)-x
Perform ADC(2)-x calculation.
ADC(3)
Perform ADC(3) calculation.
SOS-ADC(2)
Perform spin-opposite scaled ADC(2)-s calculation.
SOS-ADC(2)-x
Perform spin-opposite scaled ADC(2)-x calculation.
CVS-ADC(1)
Perform ADC(1) calculation of core excitations.
CVS-ADC(2)
Perform ADC(2)-s calculation of core excitations.
CVS-ADC(2)-x
Perform ADC(2)-x calculation of core excitations.

RECOMMENDATION:

None

EE_STATES

Controls the number of excited states to calculate.

TYPE:

INTEGER/ARRAY

DEFAULT:

0
Do not perform an ADC calculation

OPTIONS:

$n>0$
Number of states to calculate for each irrep or
$[{n}_{1},{n}_{2},\mathrm{\dots}]$
Compute ${n}_{1}$ states for the first irrep, ${n}_{2}$ states for the second irrep, …

RECOMMENDATION:

Use this variable to define the number of excited states in case of
unrestricted or open-shell calculations. In restricted calculations it can also
be used, if neither EE_SINGLETS nor EE_TRIPLETS is given.
Then, it has the same effect as setting EE_SINGLETS.

EE_SINGLETS

Controls the number of singlet excited states to calculate.

TYPE:

INTEGER/ARRAY

DEFAULT:

0
Do not perform an ADC calculation of singlet excited states

OPTIONS:

$n>0$
Number of singlet states to calculate for each irrep or
$[{n}_{1},{n}_{2},\mathrm{\dots}]$
Compute ${n}_{1}$ states for the first irrep, ${n}_{2}$
states for the second irrep, …

RECOMMENDATION:

Use this variable to define the number of excited states in case of restricted
calculations of singlet states. In unrestricted calculations it can also be
used, if EE_STATES not set. Then, it has the same effect as setting
EE_STATES.

EE_TRIPLETS

Controls the number of triplet excited states to calculate.

TYPE:

INTEGER/INTEGER ARRAY

DEFAULT:

0
Do not perform an ADC calculation of triplet excited states

OPTIONS:

$n>0$
Number of triplet states to calculate for each irrep or
$[{n}_{1},{n}_{2},\mathrm{\dots}]$
Compute ${n}_{1}$ states for the first irrep, ${n}_{2}$
states for the second irrep, …

RECOMMENDATION:

Use this variable to define the number of excited states in case of restricted
calculations of triplet
states.

CC_SYMMETRY

Activates point-group symmetry in the ADC calculation.

TYPE:

LOGICAL

DEFAULT:

TRUE
If the system possesses any point-group symmetry.

OPTIONS:

TRUE
Employ point-group symmetry
FALSE
Do not use point-group symmetry

RECOMMENDATION:

None

ADC_PROP_ES

Controls the calculation of excited state properties (currently only dipole moments).

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Calculate excited state properties.
FALSE
Do not compute state properties.

RECOMMENDATION:

Set to TRUE, if properties are required.

ADC_PROP_ES2ES

Controls the calculation of transition properties between excited states (currently only transition dipole moments and oscillator strengths), as well as
the computation of two-photon absorption cross-sections of excited states
using the sum-over-states expression.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Calculate state-to-state transition properties.
FALSE
Do not compute transition properties between excited states.

RECOMMENDATION:

Set to TRUE, if state-to-state properties or sum-over-states two-photon
absorption cross-sections are required.

ADC_PROP_TPA

Controls the calculation of two-photon absorption cross-sections of excited states using
matrix inversion techniques.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Calculate two-photon absorption cross-sections.
FALSE
Do not compute two-photon absorption cross-sections.

RECOMMENDATION:

Set to TRUE, if to obtain two-photon absorption cross-sections.

STATE_ANALYSIS

Controls the analysis and export of excited state densities and orbitals
(see 11.2.6 for details).

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Perform excited state analyses.
FALSE
No excited state analyses or export will be performed.

RECOMMENDATION:

Set to TRUE, if detailed analysis of the excited states is required
or if density or orbital plots are needed.

ADC_C_T

Set the spin-opposite scaling parameter ${c}_{T}$ for an SOS-ADC(2) calculation.
The parameter value is obtained by multiplying the given integer by ${10}^{-3}$.

TYPE:

INTEGER

DEFAULT:

1300
Optimized value ${c}_{T}=1.3$.

OPTIONS:

$n$
Corresponding to $n\cdot {10}^{-3}$

RECOMMENDATION:

Use the default.

ADC_C_C

Set the spin-opposite scaling parameter ${c}_{c}$ for the ADC(2) calculation.
The parameter value is obtained by multiplying the given integer by ${10}^{-3}$.

TYPE:

INTEGER

DEFAULT:

1170
Optimized value ${c}_{c}=1.17$ for ADC(2)-s or
1000
${c}_{c}=1.0$ for ADC(2)-x

OPTIONS:

$n$
Corresponding to $n\cdot {10}^{-3}$

RECOMMENDATION:

Use the default.

ADC_C_X

Set the spin-opposite scaling parameter ${c}_{x}$ for the ADC(2)-x calculation.
The parameter value is obtained by multiplying the given integer by ${10}^{-3}$.

TYPE:

INTEGER

DEFAULT:

1300
Optimized value ${c}_{x}=0.9$ for ADC(2)-x.

OPTIONS:

$n$
Corresponding to $n\cdot {10}^{-3}$

RECOMMENDATION:

Use the default.

ADC_NGUESS_SINGLES

Controls the number of excited state guess vectors which are single excitations. If the
number of requested excited states exceeds the total number of guess vectors (singles and
doubles), this parameter is automatically adjusted, so that the number of guess vectors
matches the number of requested excited states.

TYPE:

INTEGER

DEFAULT:

Equals to the number of excited states requested.

OPTIONS:

$n$
User-defined integer.

RECOMMENDATION:

ADC_NGUESS_DOUBLES

Controls the number of excited state guess vectors which are double excitations.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
User-defined integer.

RECOMMENDATION:

ADC_DO_DIIS

Activates the use of the DIIS algorithm for the calculation of ADC(2) excited states.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Use DIIS algorithm.
FALSE
Do diagonalization using Davidson algorithm.

RECOMMENDATION:

None.

ADC_DIIS_START

Controls the iteration step at which DIIS is turned on.

TYPE:

INTEGER

DEFAULT:

1

OPTIONS:

$n$
User-defined integer.

RECOMMENDATION:

Set to a large number to switch off DIIS steps.

ADC_DIIS_SIZE

Controls the size of the DIIS subspace.

TYPE:

INTEGER

DEFAULT:

7

OPTIONS:

$n$
User-defined integer

RECOMMENDATION:

None

ADC_DIIS_MAXITER

Controls the maximum number of DIIS iterations.

TYPE:

INTEGER

DEFAULT:

50

OPTIONS:

$n$
User-defined integer.

RECOMMENDATION:

Increase in case of slow convergence.

ADC_DIIS_ECONV

Controls the convergence criterion for the excited state energy during DIIS.

TYPE:

INTEGER

DEFAULT:

6
Corresponding to ${10}^{-6}$

OPTIONS:

$n$
Corresponding to ${10}^{-n}$

RECOMMENDATION:

None

ADC_DIIS_RCONV

Convergence criterion for the residual vector norm of the excited state during DIIS.

TYPE:

INTEGER

DEFAULT:

6
Corresponding to ${10}^{-6}$

OPTIONS:

$n$
Corresponding to ${10}^{-n}$

RECOMMENDATION:

None

ADC_DAVIDSON_MAXSUBSPACE

Controls the maximum subspace size for the Davidson procedure.

TYPE:

INTEGER

DEFAULT:

$5\times $ the number of excited states to be calculated.

OPTIONS:

$n$
User-defined integer.

RECOMMENDATION:

Should be at least $2-4\times $ the number of excited states to calculate. The
larger the value the more disk space is required.

ADC_DAVIDSON_MAXITER

Controls the maximum number of iterations of the Davidson procedure.

TYPE:

INTEGER

DEFAULT:

60

OPTIONS:

$n$
Number of iterations

RECOMMENDATION:

Use the default unless convergence problems are encountered.

ADC_DAVIDSON_CONV

Controls the convergence criterion of the Davidson procedure.

TYPE:

INTEGER

DEFAULT:

$6$
Corresponding to ${10}^{-6}$

OPTIONS:

$n\le 12$
Corresponding to ${10}^{-n}$.

RECOMMENDATION:

Use the default unless higher accuracy is required or convergence problems are encountered.

ADC_DAVIDSON_THRESH

Controls the threshold for the norm of expansion vectors to be added
during the Davidson procedure.

TYPE:

INTEGER

DEFAULT:

Twice the value of ADC_DAVIDSON_CONV, but at maximum ${10}^{-14}$.

OPTIONS:

$n\le 14$
Corresponding to ${10}^{-n}$

RECOMMENDATION:

Use the default unless convergence problems are encountered. The threshold
value ${10}^{-n}$ should always be smaller than the convergence criterion
ADC_DAVIDSON_CONV.

ADC_PRINT

Controls the amount of printing during an ADC calculation.

TYPE:

INTEGER

DEFAULT:

1
Basic status information and results are printed.

OPTIONS:

0
Quiet: almost only results are printed.
1
Normal: basic status information and results are printed.
2
Debug: more status information, extended information on timings.
…

RECOMMENDATION:

Use the default.

ADC_CVS

Activates the use of the CVS approximation for the calculation of CVS-ADC
core-excited states.

TYPE:

LOGICAL

DEFAULT:

FALSE

OPTIONS:

TRUE
Activates the CVS approximation.
FALSE
Do not compute core-excited states using the CVS approximation.

RECOMMENDATION:

Set to TRUE, if to obtain core-excited states for the simulation of
X-ray absorption spectra. In the case of TRUE, the *$rem* variable
CC_REST_OCC has to be defined as well.

CC_REST_OCC

Sets the number of restricted occupied orbitals including active core occupied
orbitals.

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

$n$
Restrict $n$ energetically lowest occupied orbitals to correspond to the
active core space.

RECOMMENDATION:

*Example:* cytosine with the molecular formula C${}_{4}$H${}_{5}$N${}_{3}$O
includes one oxygen atom. To calculate O 1s core-excited states, $n$ has to be
set to 1, because the 1s orbital of oxygen is the energetically lowest. To
obtain the N 1s core excitations, the integer $n$ has to be set to 4, because
the 1s orbital of the oxygen atom is included as well, since it is
energetically below the three 1s orbitals of the nitrogen atoms. Accordingly,
to simulate the C 1s spectrum of cytosine, $n$ must be set to 8.

SF_STATES

Controls the number of excited spin-flip states to calculate.

TYPE:

INTEGER

DEFAULT:

0
Do not perform a SF-ADC calculation

OPTIONS:

$n>0$
Number of states to calculate for each irrep or
$[{n}_{1},{n}_{2},\mathrm{\dots}]$
Compute ${n}_{1}$ states for the first irrep,
${n}_{2}$ states for the second irrep, …

RECOMMENDATION:

Use this variable to define the number of excited states in the
case of a spin-flip calculation. SF-ADC is available for ADC(2)-s,
ADC(2)-x and ADC(3).

Keywords for SS-PCM control in *$pcm*:

EQSOLV

Main switch of the self-consistent SS-PCM procedure.

INPUT SECTION: *$pcm*

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
No self-consistent SS-PCM.
1
Single SS-PCM calculation (SCF+ADC) with the solvent field found on disk.
$n>$1
Do a maximum of $n$ automatic solvent-field iterations.

RECOMMENDATION:

We recommend to use 15 steps max. Typical convergence is 3-5 steps. In
difficult cases 6-12. If the solvent-field iteration do not converge in 15
steps, something is wrong.
*Also make sure that a solvent field has
been stored on disk by a previous job.*

EQSTATE

Specifies the state for which the solvent field is to be optimized.

INPUT SECTION: *$pcm*

TYPE:

INTEGER

DEFAULT:

0

OPTIONS:

0
MP2 ground state (for PTED approach)
1
energetically lowest excited state
2
2nd lowest excited state
…

RECOMMENDATION:

Given that only one class of excited states is calculated, the state will be
selected according to its energetic position shown in the “Exited-State
Summary” of the output file. A maximum of 99 states is stored and can be
selected.

EQS_CONV

Controls the convergence of the solvent-field iterations by setting the
convergence criteria (a mixture of SCF energy and charge-vector). SCF energy
criterion computes as ${10}^{-\mathrm{value}}$ eH

INPUT SECTION: *$pcm*

TYPE:

INTEGER

DEFAULT:

SCF_CONVERGENCE$-4=4$

OPTIONS:

3
May be sufficient for emission energies
4
Assured converged total energies (2.7 meV)
5
Really tight

RECOMMENDATION:

Use the default.

EQS_REF

Allows to specify which state is to be treated as the reference state in the
ADC part of the calculation. Does in contrast to EQSTATE not affect
which solvent field is loaded in the SCF step. Only has to be used when
singlets are computed in the solvent field of a triplet reference. Note that
(converged) singlets states are always counted before triplets, and thus to
select ${T}_{1}$ in a calculation with EE_SINGLETS = 2 this has to be set
to 3.

INPUT SECTION: *$pcm*

TYPE:

INTEGER

DEFAULT:

Same as EQSTATE

OPTIONS:

1
First excited state
2
Second excited state
…

RECOMMENDATION:

Only needed when computing singlet states in the solvent field of a triplet reference.