#### Abstract

In this research paper, we will compute the topological indices (degree based) such as the ordinary generalized geometric-arithmetic (OGA) index, first and second Gourava indices, first and second hyper-Gourava indices, general Randic´ index , harmonic index, general version of the harmonic index, atom-bond connectivity (ABC) index, SK, SK_{1}, and SK_{2} indices, sum-connectivity index, general sum-connectivity index, and first general Zagreb and forgotten topological indices for various types of chemical networks such as the subdivided polythiophene network, subdivided hexagonal network, subdivided backbone DNA network, and subdivided honeycomb network. The discussion on the aforementioned networks will give us very remarkable results by using the aforementioned topological indices.

#### 1. Introduction

The branch of mathematics that is related to the study of implementation of chemistry and graph theory together is called chemical graph theory. This theory is used to model the molecules of a chemical compound mathematically. This theory helps us to understand the physical properties of that chemical/molecular compound. In this theory, we construct the structure of a chemical compound in the form of a graph. In chemical graph theory, atoms are used as nodes, and bonds between the atoms are utilized as edges. A topological index is a numerical parameter of a graph that explains its topology. The topological index is also called a molecular descriptor and a connectivity index. It is obtained by transforming the chemical information into a numerical quantity. Topological indices are used as molecular descriptors in the construction of quantitative structure-activity relationships and quantitative structure-property relationships as well. The theoretical models such as quantitative structure-activity relationships (QSARs) relate the quantitative measure of a chemical structure to a biological property or a physical property, and quantitative structure-property relationships (QSPRs) relate mathematically physical/chemical properties to the structure of a molecule. Topological indices such as ordinary generalized geometric-arithmetic (OGA) index, first and second Gourava indices, first and second hyper-Gourava indices, general Randic index , harmonic index, general version of harmonic index [1, 2], atom-bond connectivity (ABC) index [3, 4], SK, SK_{1}, and SK_{2} indices, sum-connectivity index, general sum-connectivity index, and first general Zagreb [5] and forgotten topological indices have very significant roles in QSAR and QSPR studies and are used to discuss the bioactivity of molecular structures.

In 2009, D. Vukičević and B. Furtula established the first GA index in [6–11]. The first geometric-arithmetic (GA) index of a graph was calculated by

An ordinary geometric-arithmetic index of was produced in 2011 in [12] and formulated by, for each positive real number *k*,

In 2017, V. R. Kulli proposed the first and second Gourava and hyper-Gourava indices in [13, 14]. The first and second Gourava and hyper-Gourava indices of a graph were formulated by

In 1975, Randic´ index [15–17] was introduced by Milan Randic´. It is often used in chemoinformatics to investigate the compounds of chemicals. The Randic´ index is also called “the connectivity index of the graph” and formulated bywhere *d*_{u} and are the degrees of the nodes.

Later, Bollobás and Erdos furnished its generalized version for , where ∈ *R*, known as the general Randic´ index [18–21] defined as

In 2012, L. Zhong described the harmonic index in [22, 23], and it is given by

In 2015, L. Yan introduced the general version of the harmonic index in [24] and defined by

In 2008, Ernesto¨ Estrada et al. [25, 26] introduced a new topological index, named atom-bond connectivity (ABC) index, calculated by

The ABC index is an excellent valuable index in the formation of heat in alkanes [25, 26].

*Definition 1. *For a graph , the SK index [27] can be computed byLet be the degrees of nodes and *h* in , respectively.

*Definition 2. *For a graph , the SK_{1} index can be computed byLet be the degrees of nodes and *h* in , respectively.

*Definition 3. *For a graph , the SK_{2} index can be computed byLet be the degrees of nodes and *h* in , respectively.

In 2009, B. Lučić proposed the sum-connectivity index in [28] calculated byIn 2010, B. Zhou and Trinajstić furnished an index named general sum-connectivity index in [24, 29] and formulated as follows:In 2005, X. Li and J. Zheng produced the generalized form of the ﬁrst Zagreb index by calling it the “ﬁrst general Zagreb index.” The first general Zagreb index [30–35] of a graph was computed by ; *k* belongs to *R*, and *k* ≠ 0 and *k* ≠ 1.

In 2015, Boris Furtula and Ivan Gutman discovered an index named as “forgotten topological index” [36–38] and computed as

#### 2. Topological Indices on Certain Chemical Graphs

In this part of the research paper, we will compute the topological indices (degree based) such as ordinary generalized geometric-arithmetic (OGA) index, first and second Gourava indices, first and second hyper-Gourava indices, general Randic index , harmonic index, general version of harmonic index, atom-bond connectivity (ABC) index, SK, SK_{1}, and SK_{2} indices, sum-connectivity index, general sum-connectivity index, first general Zagreb index, and forgotten topological indices for various types of chemical networks such as subdivided polythiophene network, subdivided hexagonal network, subdivided backbone DNA network, and subdivided honeycomb network.

##### 2.1. Results for the Subdivided Polythiophene Network

Polythiophenes are rings with five elements having one heteroatom together with their benzo and other carbocylic. Polythiophene is used in electronic devices such as water purification devices, biosensors, and light-emitting diodes and in hydrogen storage [39]. In a subdivided polythiophene network, shown in Figure 1, we insert another vertex (degree 2) in every edge of . In this way, we get a subdivided polythiophene network. In this section, we compute the subdivided polythiophene network using the above-defined topological indices. In the subdivided polythiophene network SPLY_{n}, we have the number of nodes 11*n* − 1 and edges 12*n* − 2. A subdivided polythiophene network for *n* = 5 is shown in Figure 1. We get two kinds of edges (degree based) that are (2, 2) and (2, 3). Table 1 gives us two types of edges. A subdivided polythiophene network SPLY_{5} is displayed in Figure 1.

Theorem 1. *For the subdivided polythiophene network, SPLY _{n}, the ordinary generalized geometric-arithmetic index is calculated by*

*Proof. *By letting as a subdivided polythiophene network SPLY_{n}, from Table 1, we knowand by doing some calculations, we get

Theorem 2. *For the subdivided polythiophene network, SPLY _{n}, the first and second Gourava indices are calculated by and .*

*Proof. *By letting as a subdivided polythiophene network SPLY_{n}, from Table 1, we knowand by doing some calculations, we get

Theorem 3. *For the subdivided polythiophene network, SPLY _{n}, the first and second hyper-Gourava indices are calculated by and .*

*Proof. *By letting as a subdivided polythiophene network, SPLY_{n}, from Table 1, we knowand by doing some calculations, we get , and

Theorem 4. *For the subdivided polythiophene network, SPLY _{n}, the general Randic´ index is calculated by*

*Proof. *By letting as a subdivided polythiophene network SPLY_{n} of *n* dimensions, we have the number of nodes and edges in SPLY_{n} as and , respectively.

We know thatfor . Case 1: if *γ* = −1, the application of Randic´ index using (23). From Table 1, we know . By doing some calculations, we get Case 2: if *γ* = − , the application of Randic´ index using (23), and by doing some calculations, we get Case 3: if *γ* = , the application of Randic´ index using (23), and by doing some calculations, we get Case 4: if *γ* = 1, the application of Randic´ index using (23), and by doing some calculations, we get .

Theorem 5. *For the subdivided polythiophene network, SPLY _{n}, the harmonic index is calculated by*

*Proof. *By letting as a subdivided polythiophene network SPLY_{n}, from Table 1, we knowand by doing some calculations, we get

Theorem 6. *For the subdivided polythiophene network, SPLY _{n}, the general version of the harmonic index is calculated by*

*Proof. *By letting as a subdivided polythiophene network SPLY_{n}, from Table 1, we knowand by doing some calculations, we get

Theorem 7. *For the subdivided polythiophene network, SPLY _{n}, the atom-bond connectivity index is calculated by*

*Proof. *By letting as a subdivided polythiophene network SPLY_{n}, from Table 1, we knowand by doing some calculations, we get

Theorem 8. *For the subdivided polythiophene network, SPLY _{n}, SK, SK_{1}, and SK_{2} indices are calculated by , and , respectively.*

*Proof. *By letting as a subdivided polythiophene network SPLY_{n}, from Table 1, we knowand by doing some calculations, we get

Theorem 9. *For the subdivided polythiophene network, SPLY _{n}, the sum-connectivity index is calculated by*

*Proof. *By letting as a subdivided polythiophene network SPLY_{n}, from Table 1, we knowand by doing some calculations, we get

Theorem 10. *For the subdivided polythiophene network, SPLY _{n}, the general sum-connectivity index is calculated by*

*Proof. *By letting as a subdivided polythiophene network SPLY_{n}, from Table 1, we knowand by doing some calculations, we get

Theorem 11. *For the subdivided polythiophene network, SPLY _{n}, the first general Zagreb index is calculated by*

*Proof. *By letting as a subdivided polythiophene network SPLY_{n}, from Table 1, we knowand by doing some calculations, we get

Theorem 12. *For the subdivided polythiophene network, SPLY _{n}, the forgotten index is calculated by*

*Proof. *By letting as a subdivided polythiophene network SPLY_{n}, from Table 1, we knowand by doing some calculations, we get

##### 2.2. Results for the Subdivided Hexagonal Network

We construct a subdivided hexagonal network shown in Figure 2 by adding a new vertex in each edge. For this process, a triangular tiling is used. In this way, an *n*-dimensional subdivided hexagonal network is obtained and denoted by SHX_{n}. A subdivided hexagonal network for *n* = 6 is shown in Figure 2, whereas *n* shows the number of nodes. The order of SHX_{n} is 12*n*^{2} − 18*n* + 7 for *n* > 1, and the size is 18*n*^{2} − 30*n* + 12 for *n* > 1. After the subdivision of this network, we have three types of edges that are (2, 3), (2, 4), and (2, 6). The division of edges is shown in Table 2. A subdivided hexagonal network SHX_{6} is displayed in Figure 2.

Theorem 13. *For the subdivided hexagonal network, SHX _{n}, the ordinary generalized geometric-arithmetic index is calculated by*

*Proof. *By letting as a subdivided hexagonal network SHX_{n}, from Table 2, we knowand by doing some calculations, we get

Theorem 14. *For the subdivided hexagonal network, SHX _{n}, the first and second Gourava indices are calculated by*

*Proof. *By letting as a subdivided hexagonal network SHX_{n}, from Table 2, we knowand by doing some calculations, we get

Theorem 15. *For the subdivided hexagonal network, SHX _{n}, the first and second hyper-Gourava indices are calculated by and .*

*Proof. *By letting as a subdivided hexagonal network SHX_{n}, from Table 2, we knowand by doing some calculations, we get

Theorem 16. *For the subdivided hexagonal network, SHX _{n}, n > 1, the general Randic´ index is calculated by*

*Proof. *By letting as a subdivided hexagonal network SHX_{n} of *n* dimensions, we have the number of nodes and edges in SHX_{n} as for *n* *>* 1 and for *n* *>* 1, respectively. We know thatfor . Case 1: if *γ* = −1, the application of Randic´ index using (63). From Table 2, we know By doing some calculations, we get Case 2: if *γ* = − , the application of Randic´ index using (63), By doing some calculations, we get Case 3: if *γ* = , the application of Randic´ index using (63), By doing some calculations, we get Case 4: if *γ* = 1, the application of Randic´ index using (63),By doing some calculations, we get

Theorem 17. *For the subdivided hexagonal network, SHX _{n}, the harmonic index is calculated by*

*Proof. *By letting as a subdivided hexagonal network SHX_{n}, from Table 2, we knowBy doing some calculations, we get

Theorem 18. *For the subdivided hexagonal network, SHX _{n}, the general version of the harmonic index is calculated by*

*Proof. *By letting as a subdivided hexagonal network SHX_{n}, from Table 2, we knowBy doing some calculations, we get

Theorem 19. *For the subdivided hexagonal network, SHX _{n}, the atom-bond connectivity index is calculated by*

*Proof. *By letting as a subdivided hexagonal network SHX_{n}, from Table 2, we knowand by doing some calculations, we get

Theorem 20. *For the subdivided hexagonal network, SHX _{n}, SK, SK_{1}, and SK_{2} indices are calculated by , respectively.*

*Proof. *By letting as a subdivided hexagonal network SHX_{n}, from Table 2, we knowand by doing some calculations, we get

Theorem 21. *For the subdivided hexagonal network, SHX _{n}, the sum-connectivity index is calculated by*

*Proof. *By letting as a subdivided hexagonal network SHX_{n}, from Table 2, we knowand by doing some calculations, we get

Theorem 22. *For the subdivided hexagonal network, SHX _{n}, the general sum-connectivity index is calculated by*

*Proof. *By letting as a subdivided hexagonal network SHX_{n}, from Table 2, we knowand by doing some calculations, we get

Theorem 23. *For the subdivided hexagonal network, SHX _{n}, the first general Zagreb index is calculated by*

*Proof. *By letting as a subdivided hexagonal network SHX_{n}, from Table 2, we knowand by doing some calculations, we get

Theorem 24. *For the subdivided hexagonal network, SHX _{n}, the forgotten index is calculated by*

*Proof. *By letting as a subdivided hexagonal network SHX_{n}, from Table 2, we knowand by doing some calculations, we get

##### 2.3. Results for the Subdivided Backbone DNA Network

The structure of DNA is called a double helix as it is made of two strands that wind around each other that looks like a staircase [40]. Each strand has a backbone made of deoxyribose, sugar, and a phosphate group. These sugar and phosphates make up the backbone, while the nitrogen bases are found in the centre and hold the two strands together. There are 4 bases attached to each sugar which are adenine, cytosine, guanine, and thymine. Both ends of DNA have a number, i.e., one end is ´5 and the other is ´3. In a subdivided backbone DNA network, shown in Figure 3, we insert another node (degree 2) in each edge of . In this way, we get a subdivided backbone DNA network of *n* dimensions. A subdivided backbone DNA network for *n* = 4 is displayed in Figure 3. A subdivided backbone DNA network is symbolized as SBB_{DNA}(*n*). The order and size of SBB_{DNA}(*n*) are 15*n *− 5 and 16*n *− 6, respectively. We obtain two types of edges (degree based) that are (2, 2) and (2, 3). Table 3 gives us two kinds of edges. A subdivided backbone DNA network SBB_{DNA}(4) is shown in Figure 3.

Theorem 25. *For the subdivided backbone DNA network, SBB _{DNA}(n), the ordinary generalized geometric-arithmetic index is calculated by*

*Proof. *By letting as a subdivided backbone DNA network SBB_{DNA}(*n*), from Table 3, we knowand by doing some calculations, we get

Theorem 26. *For the subdivided backbone DNA network, SBB _{DNA}(n), the first and second Gourava indices are calculated by and .*

*Proof. *By letting as a subdivided backbone DNA network SBB_{DNA}(*n*), from Table 3, we knowand by doing some calculations, we get

Theorem 27. *For the subdivided backbone DNA network, SBB _{DNA}(n), the first and second hyper-Gourava indices are calculated by*

*Proof. *By letting as a subdivided backbone DNA network SBB_{DNA}(*n*), from Table 3, we knowand by doing some calculations, we get

Theorem 28. *For the subdivided backbone DNA network, SBB _{DNA}(n), the general Randic´ index is calculated by*

*Proof. *By letting as a subdivided backbone DNA network SBB_{DNA}(*n*) of *n* dimensions, we have the order and size of in SBB_{DNA}(*n*) as and , respectively.

We know thatfor . Case 1: if *γ* = −1, the application of Randic´ index using (107). From Table 3, we know . By doing some calculations, we get Case 2: if *γ* = −, the application of Randic´ index using (107), and by doing some calculations, we get Case 3: if *γ* = , the application of Randic´ index using (107), and by doing some calculations, we get Case 4: if *γ* = 1, the application of Randic´ index using (107), and by doing some calculations, we get .

Theorem 29. *For the subdivided backbone DNA network, SBB _{DNA}(n), the harmonic index is calculated by*

*Proof. *By letting as a subdivided backbone DNA network SBB_{DNA}(*n*), from Table 3, we knowand by doing some calculations, we get

Theorem 30. *For the subdivided backbone DNA network, SBB _{DNA}(n), the general version of the harmonic index is calculated by*

*Proof. *By letting as a subdivided backbone DNA network SBB_{DNA}(*n*), from Table 3, we knowand by doing some calculations, we get

Theorem 31. *For the subdivided backbone DNA network, SBB _{DNA}(n), the atom-bond connectivity index is calculated by*

*Proof. *By letting as a subdivided backbone DNA network SBB_{DNA}(*n*), from Table 3, we knowBy doing some calculations, we get

Theorem 32. *For the subdivided backbone DNA network, SBB _{DNA}(n), SK, SK_{1}, and SK_{2} indices are calculated by and , respectively.*

*Proof. *By letting as a subdivided backbone DNA network SBB_{DNA}(*n*), from Table 3, we knowBy doing some calculations, we get