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