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
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.
For IP- and EA-ADC calculations, the IP_STATES,
EOM_IP_ALPHA, EOM_IP_BETA, EA_STATES,
EOM_EA_ALPHA and EOM_EA_BETA are available to control the number and
type of ionized or electron-attached states to calculate. IP_STATES and
EA_STATES should be used in case of restricted calculations, while the
EOM_[IP/EA]_[ALPHA/BETA] keywords control the number of - and
-ionized and -electron-attached states to calculate in case of unrestricted
or open-shell calculations.
All $rem variables to set the number of excited, ionized or electron-attached 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 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 symmetric by setting
CC_SYMMETRY = FALSE.
For ADC methods, in combination with a smoothed Voronoi-CAP
(CAP_TYPE = 2) or a spherical CAP (CAP_TYPE = 0),
this keyword controls the lower limit for a series of CAP onsets,
where the upper limit is given by CAP_X_END. The parameter value in a.u. is
obtained by multiplying the given integer by . In this case, the onset value defines the
region around the molecule with zero CAP strength. In combination with a
cuboid CAP (CAP_TYPE = 1) or in general for other electronic
structure methods (see 7.10.8 for further details), this keyword
controls the CAP onset in direction.
Usually, values of 2000 to 4000 (corresponding to onset values between 2.0 and 4.0 a.u.)
give reasonable results.
Controls the calculation of transition properties between excited, ionized or
electron-attached states (currently only transition dipole moments and oscillator strengths). For ADC for
-electron excitations, this keyword also controls
the computation of two-photon absorption cross-sections of excited states
using the sum-over-states expression.
Set to TRUE, if state-to-state properties (ADC, IP-ADC, EA-ADC) or sum-over-states two-photon
absorption cross-sections (only ADC) are required.
Controls the number of excited state guess vectors which are single excitations, one-hole
ionizations and one-particle electron-attachments in case of ADC, IP-ADC and EA-ADC,
respectively. 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.
Equals to the number of excited states requested.
Increase if there are convergence problems.
Sets the number of restricted occupied orbitals including active core occupied
Restrict energetically lowest occupied orbitals to correspond to the
active core space.
Example: cytosine with the molecular formula CHNO
includes one oxygen atom. To calculate O 1s core-excited states, 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 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, must be set to 8.