# 12.1. Introduction¶

This section describes some of the general characteristics of RMG’s databases.

## 12.1.1. Group Definitions¶

The main section in many of RMG’s databases are the ‘group’ definitions. Groups are adjacency lists that describe structures around the reacting atoms. Between the adjacency list’s index number and atom type, a starred number is inserted if the atom is a reacting atom.

Because groups typically do not describe entire molecules, atoms may appear to be lacking full valency. When this occurs, the omitted bonds are allowed to be anything. An example of a primary carbon group from H-Abstraction is shown below. The adjacency list defined on the left matches any of the three drawn structures on the right (the numbers correspond to the index from the adjacency list).

Atom types describe atoms in group definitions. The table below shows all atoms types in RMG.

Atom Type Chemical Element Bonding
R Any No requirements
R!H Any except hydrogen No requirements
H Hydrogen No requirements
C Carbon No requirements
Ca Carbon Atomic carbon with two lone pairs and no bonds
Cs Carbon Up to four single bonds
Csc Carbon Up to three single bonds, charged +1
Cd Carbon One double bond (to any atom other than O or S), up to two single bonds
Cdc Carbon One double bond, up to one single bond, charged +1
CO Carbon One double bond to an oxygen atom, up to two single bonds
CS Carbon One double bond to an sulfur atom, up to two single bonds
Cdd Carbon Two double bonds
Ct Carbon One triple bond, up to one single bond
Cb Carbon Two benzene bonds, up tp one single bond
Cbf Carbon Three benzene bonds (fused aromatics)
C2s Carbon One lone pair, up to two single bonds
C2sc Carbon One lone pair, up to three single bonds, charged -1
C2d Carbon One lone pair, one double bond
C2dc Carbon One lone pair, one double bond, up to one single bond, charge -1
C2tc Carbon One lone pair, one triple bond, charged -1
N Nitrogen No requirements
N0sc Nitrogen Three lone pairs, up to one single bond, charged -2
N1s Nitrogen Two lone pairs, up to one single bond
N1sc Nitrogen Two lone pairs, up to two single bonds, charged -1
N1dc Nitrogen Two lone pairs, one double bond, charged -1
N3s Nitrogen One lone pair, up to three single bonds
N3d Nitrogen One lone pair, one double bond, up to one single bond
N3t Nitrogen One lone pair, one triple bond
N3b Nitrogen One lone pair, two aromatic bonds
N5sc Nitrogen No lone pairs, up to four single bonds, charged +1
N5dc Nitrogen No lone pairs, one double bond, up to two single bonds, charged +1
N5ddc Nitrogen No lone pairs, two double bonds, charged +1
N5dddc Nitrogen No lone pairs, three double bonds, charged -1
N5t Nitrogen No lone pairs, one triple bond, up to two single bonds
N5tc Nitrogen No lone pairs, one triple bond, up to one single bond, charged +1
N5b Nitrogen No lone pairs, two aromatic bonds, up to one single bond
O Oxygen No requirements
Oa Oxygen Atomic oxygen with three lone pairs and no bonds
O0sc Oxygen Three lone pairs, up to one single bond, charged -1
O0dc Oxygen Three lone pairs, one double bond, charged -2
O2s Oxygen Two lone pairs, up to two single bonds
O2sc Oxygen Two lone pairs, up to one single bond, charged +1
O2d Oxygen Two lone pairs, one double bond
O4sc Oxygen One lone pair, up to three single bonds, charged +1
O4dc Oxygen One lone pair, one double bond, up to one single bond, charged +1
O4tc Oxygen One lone pair, one triple bond, charged +1
Si Silicon No requirements
Sis Silicon Up to four single bonds
Sid Silicon One double bond (not to O), up to two single bonds
SiO Silicon One double bond to an oxygen atom, up to two single bonds
Sidd Silicon Two double bonds
Sit Silicon One triple bond, up to one single bond
Sib Silicon Two benzene bonds, up tp one single bond
Sibf Silicon Three benzene bonds (fused aromatics)
S Sulfur No requirements
Sa Sulfur Atomic sulfur with three lone pairs and no bonds
S0sc Sulfur Three lone pairs, up to once single bond, charged -1
S2s Sulfur Two lone pairs, up to two single bonds
S2sc Sulfur Two lone pairs, up to three single bonds, charged -1/+1
S2d Sulfur Two lone pairs, one double bond
S2dc Sulfur Two lone pairs, one to two double bonds, up to one single bond, charged -1
S2tc Sulfur Two lone pairs, one triple bond, charged -1
S4s Sulfur One lone pair, up to four single bonds
S4sc Sulfur One lone pair, up to five single bonds, charged -1/+1
S4d Sulfur One lone pair, one double bond, up to two single bonds
S4dd Sulfur One lone pair, two double bonds
S4dc Sulfur One lone pair, one to three double bonds, up to three single bonds, charged -1/+1
S4b Sulfur One lone pair, two aromatic bonds
S4t Sulfur One lone pair, one triple bond, up to one single bond
S4tdc Sulfur One lone pair, one to two triple bonds, up to two double bonds, up to two single bonds, charged -1/+1
S6s Sulfur No lone pairs, up to six single bonds
S6sc Sulfur No lone pairs, up to seven single bonds, charged -1/+1
S6d Sulfur No lone pairs, one double bond, up to four single bonds
S6dd Sulfur No lone pairs, two double bonds, up to two single bonds
S6ddd Sulfur No lone pairs, up to three double bonds
S6dc Sulfur No lone pairs, one to to three double bonds, up to five single bonds, charged -1/-1
S6t Sulfur No lone pairs, one triple bond, up to three single bonds
S6td Sulfur No lone pairs, one triple bond, one double bond, up to one single bond
S6tt Sulfur No lone pairs, two triple bonds
S6tdc Sulfur No lone pairs, one to two triple bonds, up to two double bonds, up to four single bonds, charged -1/-1
Cl Chlorine No requirements
Cl1s Chlorine Three lone pairs, zero to one single bonds
I Iodine No requirements
I1s Iodine Three lone pairs, zero to one single bonds
He Helium No requirements, nonreactive
Ne Neon No requirements, nonreactive
Ar Argon No requirements, nonreactive

Additionally, groups can also be defined as unions of other groups. For example,:

label="X_H_or_Xrad_H",


## 12.1.2. Forbidden Groups¶

Forbidden groups can be defined to ban structures globally in RMG or to ban pathways in a specific kinetic family.

Globally forbidden structures will ban all reactions containing either reactants or products that are forbidden. These groups are stored in in the file located at RMG-database/input/forbiddenStructures.py.

To ban certain specific pathways in the kinetics families, a forbidden group must be created, like the following group in the intra_H_migration family:

forbidden(
label = "bridged56_1254",
group =
"""
1 *1 C 1 {2,S} {6,S}
2 *4 C 0 {1,S} {3,S} {7,S}
3    C 0 {2,S} {4,S}
4 *2 C 0 {3,S} {5,S} {8,S}
5 *5 C 0 {4,S} {6,S} {7,S}
6    C 0 {1,S} {5,S}
7    C 0 {2,S} {5,S}
8 *3 H 0 {4,S}
""",
shortDesc = u"""""",
longDesc =
u"""

""",
)


Forbidden groups should be placed inside the groups.py file located inside the specific kinetics family’s folder RMG-database/input/kinetics/family_name/ alongside normal group entries. The starred atoms in the forbidden group ban the specified reaction recipe from occurring in matched products and reactants.

In addition for forbidding groups, there is the option of forbidding specific molecules or species. Forbidding a molecule will prevent that exact structure from being generated, while forbidding a species will prevent any of its resonance structures from being generated. To specify a forbidden molecule or species, simply replace the group keyword with molecule or species:

# This forbids a molecule
forbidden(
label = "C_quintet",
molecule =
"""
multiplicity 5
1 C u4 p0
""",
shortDesc = u"""""",
longDesc =
u"""

""",
)

# This forbids a species
forbidden(
label = "C_quintet",
species =
"""
multiplicity 5
1 C u4 p0
""",
shortDesc = u"""""",
longDesc =
u"""

""",
)


## 12.1.3. Hierarchical Trees¶

Groups are ordered into the nodes of a hierarchical trees which is written at the end of groups.py. The root node of each tree is the most general group with the reacting atoms required for the family. Descending from the root node are more specific groups. Each child node is a subset of the parent node above it.

A simplified example of the trees for H-abstraction is shown below. The indented text shows the syntax in groups.py and a schematic is given underneath.

Individual groups only describe part of the reaction. To describe an entire reaction we need one group from each tree, which we call node templates or simply templates. (C_pri, O_pri_rad), (H2, O_sec_rad), and (X_H, Y_rad) are all valid examples of templates. Templates can be filled in with kinetic parameters from the training set or rules.