# Keywords¶

## Summary of all keywords¶

AllowSanityCheckWarnings
Type: Bool No Sanity checks will be performed on the setup. If this option is on, only warnings are printed. If not the program will stop on warnings.
Capping
Type: Block This block is about capping details. Capping occurs with hydrogen atoms when a bond is broken between an atom inside the region and one outside.
AllowHighBondOrders
Type: Bool No Allows capping of interregional aromatic, double and triple bonds. This is normally not a good idea, since the capping is done with hydrogen atoms.
AtomicInfoForCappingAtom
Type: String ForceField.Type=H_ ForceField.Charge=0.0 The AtomicInfo for the capping atoms. Typically a string like ForceField.Type=X much like forcefield info is entered in the System block for normal atoms.
CappingElement
Type: String H The element to be used for capping. The hydrogen atom has the advantage that it is very small.
CheckCapping
Type: Bool Yes The same outside atom can be involved in multiple capping coordinate definitions. This is not a good idea, and this will not be accepted by using this check.
Distance
Type: Float -1.0 A negative value means automatic. In that case the sum of covalent radii is used
Option
Type: Multiple Choice Fixed [Fractional, Fixed] Capping option The capping atom is always along the broken bond vector. The bond distance between the capping atom and the two atoms are obtained from covalent radii, let us call them D1H and D2H. With option=Fractional the capping is on the bond vector with the fraction D1H/(D1H+D2H). With the Fixed option it at the distance D1H from atom 1. A distance of zero always means the coordinate of the inside atom.
Energy
Type: Block This block is there to construct the energy.
Term
Type: Block True This block is there to construct the energy term. Can have multiple occurrences
Charge
Type: Float 0.0 Net charge to be used for this energy term.
EngineID
Type: String Identifier for the engine
Factor
Type: Float 1.0
Region
Type: String Identifier for the region
UseCappingAtoms
Type: Bool Yes Whether to use capping for broken bonds
Engine
Type: Block True The input for the computational (sub) engine. The header of the block determines the type of the engine. An optional second word in the header serves as the EngineID, if not present it defaults to the engine name. Currently it is not allowed to have a Hybrid engine as a sub engine.
QMMM
Type: Block This block is there to identify the QMMM engines.
Embedding
Type: Multiple Choice Electrostatic [Mechanical, Electrostatic] Determines how the QM region is embedded into the MM region. Mechanical embedding embedding can also be achieved using the Energy%Terms keywords, but the common case of a two region mechanical QM/MM embedding is easier to set up using this keyword.
MMCharge
Type: Float 0.0 Net charge to be used for the MM region.
MMEngineID
Type: String Identifier for the MM engine
QMCharge
Type: Float 0.0 Net charge to be used for the QM region.
QMEngineID
Type: String Identifier for the QM engine
QMRegion
Type: String Identifier for the QM region. The rest of the system is considered the MM region.
UseCappingAtoms
Type: Bool Yes Whether to use capping for broken bonds.
RestartSubEngines
Type: Bool Yes Save all the results of the subengines and pass those in a next geometry step or MD step.
TweakRequestForSubEngines
Type: Bool Yes Only request what is really needed, gradients and charges.