J. Nig. Soc. Phys. Sci. 5 (2023) 1371

Journal of the
Nigerian Society

of Physical
Sciences

Corrosion Inhibition Properties of Lawsone Derivatives againts
Mild Steel: A Theoretical Study

Saprizal Hadisaputra∗, Lalu Rudyat Telly Savalas

Chemistry Education Division, FKIP, University of Mataram. Jalan Majapahit 62, Mataram, 83125, Indonesia

Abstract

Theoretical studies have been carried out using DFT, ab initio MP2 and Monte Carlo (MC) simulations of corrosion inhibitors from lawsone
derivatives against carbon steel. The research focuses on studying the effect of substituent groups in the lawsone structure on the efficiency of
corrosion inhibition in mild steel. Quantum chemical parameters of lawstone inhibitors in neutral and protonated conditions have been calculated.
Fukui’s function analysis predicts that the active side of the inhibitor will be adsorbed on the mild steel surface. MC simulation is used to
understand the adsorption patterns of lawsone compounds on metal surfaces. The organic inhibitor L-NH2 has better performance as a corrosion
inhibitor for mild steel in neutral or protonated conditions.

DOI:10.46481/jnsps.2023.1371

Keywords: Lawsone, Substituents, DFT, MP2, Monte Carlo, Corrosion inhibitors

Article History :
Received: 26 January 2023
Received in revised form: 21 February 2023
Accepted for publication: 30 March 2023
Published: 14 June 2023

© 2023 The Author(s). Published by the Nigerian Society of Physical Sciences under the terms of the Creative Commons Attribution 4.0 International license

(https://creativecommons.org/licenses/by/4.0). Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Communicated by: K. Sakthipandi

1. Introduction

Metals are damaged by corrosion as a result of corrosive
environmental interactions [1, 2]. Corrosion causes significant
economic losses, and harms the environment [3, 4]. The cor-
rosion inhibitors that are currently in use are inorganic and un-
friendly to the environment. Therefore, organic inhibitors based
on eco-friendly natural ingredients prevent potential corrosion.
Plant extracts have reportedly been used as corrosion inhibitors
that are safe for the environment [4]. The majority of natu-
ral materials are highly effective inhibitors. It is because nat-
ural product molecules like alkaloids and flavaloids, which are
sources of π-electrons, also include heteroatoms N, O, and S

∗Corresponding author tel. no:
Email address: rizal@unram.ac.id (Saprizal Hadisaputra)

[4]. The natural chemicals that have adsorbed on the surface
of the metal and shield it from corrosion attack are responsi-
ble for the high value of corrosion inhibition efficiency. El-Etre
et al. investigated lawsone as corrosion inhibitors on metals in
various environments, including as acids, in experimental study
that was previously published. The figure for inhibitory effi-
ciency that was highest was 95.78% for carbon steel, followed
by 93.44% for Zn in a NaCl media and 88.77% for Ni in an
HCl medium [5,6]. In a different investigation, Dananjaya et al.
evaluated the lawstone as a corrosion inhibitor on mild steel in
an acidic media and discovered that it was 93.14% effective [5].
Theoretical investigations have shown that substituents in the
inhibitor structure can raise the value of inhibitory efficiency.

The mechanism of corrosion inhibition has frequently been
explained by theoretical investigations [7]. The challenges that

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Hadisaputra & Savalas / J. Nig. Soc. Phys. Sci. 5 (2023) 1371 2

experimental research have identified have been successfully
addressed by theoretical studies [8]. Molecular structure can
be determined using quantum chemistry techniques, which can
also be used to explain reactivity and electronic structure. The
experimental studies that have already been conducted can be
supplemented by quantum chemical computations [9]. The cur-
rent investigation focuses on the electrical characteristics of the
quantum parameters of the lawone derivative. It is thought that
substituents alter how far electrons shift inside the inhibitor,
which in turn affects how well corrosion is inhibited.

2. Methodology

2.1. Quantum Chemical Parameters

To understand experimental results and explore reaction path-
ways, quantum chemical simulations have been used extensively
[10]. The structural significance of corrosion inhibitors and ad-
sorption on metal surfaces has been satisfactorily described us-
ing DFT [11–12,13]. Gaussian 09 [14] implements for density
functional theory (DFT) and ab initio MP2 6-311++G (d,p) for
quantum chemical calculations in the gas and solution phases.
The reactivity of a molecule can be described by quantum chem-
ical characteristics. Charge population and condensed Fukui
function are two more variables that can be used to determine
local selectivity [16]. Koopmans’ theorem states that the values
of EHOMO and ELUMO are related to ionization potential I
=− EHOMO and electron affinity A=− ELUMO, respectively.
The ability of an atom or collection of atoms to draw electrons
toward itself is known as electronegativity χ= I+A2 . Atomic re-
sistance to charge transfer is measured by hardness (η) [18, 19].
The hardness value can be used to calculate by η= I−A2 . The
quantity of electrons exchanged: ∆N= χFe−χInh2(ηFe+ηInh) , where χFe
and χinh represent, respectively, the absolute electronegativi-
ties of iron and organic inhibitors. The absolute hardness of iron
and organic inhibitors, respectively, are denoted by the symbols
ηFe and ηinh. The number of electrons transported is deter-
mined using the theoretical values of Fe = 7.0 eV and Fe = 0
[20, 21]. The Fukui function can be used to calculate by f+=
q(N + 1) q (N) and f- = q(N) – q(N-1) where the charge an
atom has upon accepting electrons is denoted by q(N+1). The
charge on an atom in a neutral molecular state is defined by the
formula q(N). The charge left on an atom after it loses electrons
is known as q(N-1) [22, 23].

2.2. MC simulation Calculations

Material Studio 7.0 was used to do MC simulations [24–
25]. The interaction of lawsone derivatives with 100 water
molecules on the surface of mild steel was simulated using MC
techniques to find the configuration with the lowest adsorption
energy [26]. The Fe (110) field can be used to depict the surface
of mild steel. Because it is the most stable and has a medium
atomic density, the Fe(110) field is employed [27]. A 20 vac-
uum layer on the C axis and an 8x8 supercell were included
in the simulation box (19.859002 x 19.859002 x 34.187956)
used to simulate the Fe(110) field [28]. The water dissolving
action was simulated by adding 100 geometrically optimized

water molecules, each of the organic inhibitors (L-H, L-NH2,
L-OCH3, and L-NO2), and the Fe(110) surface to a simulated
box using the KOMPASS force field [25]. To simulate the ac-
tual corrosion environment, a MC simulation was performed.

3. Results and Discussion

The lawone was evaluated as a corrosion inhibitor on mild
steel in hydrochloric acid environment in earlier studies by Danan-
jaya et al. The weight loss strategy utilized produced a 93.14%
inhibitory efficiency score [5]. Henna plant extract, an aromatic
hydroxyl chemical, is the source of lawsone. The metal sur-
face will be able to create a more stable structure thanks to the
lawsone phenol group’s ability to transfer electrons to it. This
can inhibit redox reactions and guard against corrosion attacks
on metals [29]. In addition, both donor and electron withdraw-
ing groups have the potential to affect the value of inhibition
efficiency. First, technique validation was done in this theoreti-
cal study. To ensure the accuracy of the technique and the set of
bases employed, method validation is done. This is done so that
results from theoretical and experimental investigations can be
compared. Figure 1 depicts the lawsone’s geometric structure.
It can be contrasted with the findings of theoretical research and
an experimental X-ray study that Salunke-Gawali et al. [30]
previously reported. Table 1 shows that there is a 0.0504-unit
difference in the Bond distance. The basis sets are suitable for
application since the results of the variations in the lawsone’s
binding distances are fairly modest.

The surfaces of mild steel (Fe) can adsorb lawsone com-
pounds and substituents (NH2, OCH3, and NO2) under neutral
or protonated circumstances [31]. Electron transfer is investi-
gated by demonstrating the characteristics of molecular orbitals
[15]. EHOMO is typically correlated with an organic inhibitor’s
ability to provide metals with electrons [32]. Table 3 demon-
strates that the organic inhibitor L-NH2 has a larger EHOMO
value and a tendency to be able to donate electrons to Fe metal,
as measured by -8.6774 eV. The values for electron transport
are L-NH2, L-OCH3, L-H, and L-NO2, in that order. As op-
posed to organic inhibitors L-H, L-OCH3, and L-NO2, L-NH2
is expected to have a higher level of inhibitory efficiency.

In addition to accepting electrons from metal d-orbitals, which
results in the creation of back bonds, the value of inhibitory effi-
ciency can also be acquired by donating electrons to the empty
d-orbitals of metal ions [33]. As a result, accepting electrons
from the empty d-orbitals of metals is made easier by a lower
ELUMO value. Table 3 shows L-NH2 had the greatest ELUMO
at 0.1850 eV and L-NO2 had the lowest at -0.4789 eV. These
findings suggest that the organic inhibitors of L-NO2 are more
likely to receive electrons from the Fe d orbital, predicting a
decline in efficiency.

The reactivity of atoms and molecules can be characterized
by their ionization potential [15]. Due to the atoms’ low ion-
ization potential, they are able to donate electrons from organic
inhibitors to the metal surface by simply releasing their outer
electrons. The high ionization potential value indicates that
electrons do not easily escape from the outer shell, which means
that there is difficulty in the process of transferring electrons

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Hadisaputra & Savalas / J. Nig. Soc. Phys. Sci. 5 (2023) 1371 3

Figure 1: Structure of lawsone (R= -NH2, OCH3, NO2)

Table 1: Comparison of the crystal structure of the lawone compound in the experimental study [30] and the theoretical study of
DFT/6-311++G (d,p)

Bond (Å) Exp [30] Theory Bond (Å) Exp [30] Theory
C1-O1 1.220 1.22029 C5-C6 1.394 1.39450
C2-O2 1.264 1.34507 C5-H5 0.950 1.08516
C4-O3 1.259 1.22792 C6-C7 1.390 1.39891
C1-C9 1.483 1.48758 C6-H6 0.950 1.08654
C1-C2 1.530 1.50585 C7-C8 1.389 1.39335
C2-C3 1.388 1.35348 C7-H7 0.950 1.08638
C3-C4 1.407 1.46702 C8-C9 1.393 1.39914
C3-H3 0.950 1.08799 C8- H8 0.950 1.08522
C4-C10 1.491 1.49688 C9-C10 1.397 1.40743
C5-C10 1.392 1.39639 - - -

Table 2: Quantum chemical characteristics (in eV) of organic inhibitors in gaseous media estimated by DFT and MP2 using a
6-311++G(d,p) level of theory

Inhibitors EHOMO ELUMO ∆E I A χ η ∆N
L-H
DFT/B3LYP -7.5272 -3.4436 -4.0836 7.5272 3.4436 5.4854 2.0418 0.3709
Ab initio MP2 -9.8483 0.1905 -10.0388 9.8483 -0.1905 4.8289 5.0194 0.2163
L-NH2
DFT/B3LYP -6.2537 -3.2066 -3.0471 6.2537 3.2066 4.7302 1.5236 0.7449
Ab initio MP2 -8.7414 0.3086 -9.0500 8.7414 -0.3086 4.2164 4.5250 0.3076
PP-OCH3
DFT/B3LYP -6.6268 -3.3718 -3.2550 6.6268 3.3718 4.9993 1.6275 0.6147
Ab initio MP2 -9.2486 0.1502 -9.3988 9.2486 -0.1502 4.5492 4.6994 0.2608
PP-NO2
DFT/B3LYP -7.8570 -4.1963 -3.6607 7.8570 4.1963 6.0266 1.8304 0.2659
Ab initio MP2 -10.3033 -0.6196 -9.6837 10.3033 0.6196 5.4615 4.8419 0.1589

from organic inhibitors to the Fe surface [34]. Table 3 shows
the low ionization potential value on L-NH2 is 8.6774 eV while
the highest ionization potential value is on L-NO2 of 9.9471 eV.
The organic inhibitor L-NH2 is more reactive to metal Fe so that
it can cause a strong interaction between organic inhibitors and
metal Fe. It can be predicted that the organic inhibitor L-NH2
can increase the value of inhibition efficiency. Pan et al. have

reported that the experimental ionization potential value for 1,4-
naphthaquinone using IR LD/VUV PIMS was found to be 9.52
eV [35]. The results obtained were almost close to the ioniza-
tion potential value of the organic inhibitor L-H (lawsone) of
9.7926 eV using the ab initio method in aqueous media. There-
fore, the ab intio MP2 at 6-311++G (d,p) method is valid to
use.

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Hadisaputra & Savalas / J. Nig. Soc. Phys. Sci. 5 (2023) 1371 4

Table 3: The quantum chemical characteristics (in eV) of organic inhibitors in aqueous environments determined using DFT and
MP2 with a 6-311++G(d,p) level of theory

Inhibitors EHOMO ELUMO ∆E I A χ η ∆N
L-H
DFT/B3LYP -7.4219 -3.5035 -3.9184 7.4219 3.5035 5.4627 1.9592 0.3923
Ab initio MP2 -9.7926 0.1162 -9.9088 9.7926 -0.1162 4.8382 4.9544 0.2182
L-NH2
DFT/B3LYP -6.1835 -3.3157 -2.8678 6.1835 3.3157 4.7496 1.4339 0.7847
Ab initio MP2 -8.6774 0.1850 -8.8625 8.6774 -0.1850 4.2462 4.4312 0.3107
L-OCH3
DFT/B3LYP -6.6273 -3.4733 -3.1541 6.6273 3.4733 5.0503 1.5770 0.6182
Ab initio MP2 -9.2483 0.0465 -9.2949 9.2483 -0.0465 4.6009 4.6474 0.2581
L-NO2
DFT/B3LYP -7.8475 -4.0904 -3.7571 7.8475 4.0904 5.9690 1.8785 0.2744
Ab initio MP2 -9.9471 -0.4789 -9.4682 9.9471 0.4789 5.2130 4.7341 0.1887

Table 4: The quantum chemical characteristics (in eV) of protonated organic inhibitors determined using DFT and MP2 in a 6-
311++G(d,p) in gaseous media

Inhibitors EHOMO ELUMO ∆E I A χ η ∆N
Pronated L-H
DFT/B3LYP -11.6394 -8.2804 -3.3590 11.6394 8.2804 9.9599 1.6795 -0.8812
Ab initio MP2 -13.6748 -4.7081 -8.9667 13.6748 4.7081 9.1915 4.4834 -0.2444
Pronated L-NH2
DFT/B3LYP -10.7471 -8.1474 -2.5998 10.7471 8.1474 9.4473 1.2999 -0.9413
Ab initio MP2 -13.1058 -4.7557 -8.3501 13.1058 4.7557 8.9308 4.1750 -0.2312
Pronated L-OCH3
DFT/B3LYP -10.9319 -8.2570 -2.6749 10.9319 8.2570 9.5945 1.3374 -0.9699
Ab initio MP2 -13.4060 -4.8469 -8.5591 13.4060 4.8469 9.1264 4.2795 -0.2484
Pronated L-NO2
DFT/B3LYP -12.0519 -8.7101 -3.3418 12.0519 8.7101 10.3810 1.6709 -1.0117
Ab initio MP2 -14.0941 -5.1383 -8.9558 14.0941 5.1383 9.6162 4.4779 -0.2921

Table 5: Quantum chemical characteristics (in eV) of protonated organic inhibitors in aqueous media as computed using DFT and
MP2 in a 6-311++G(d,p) level of theory

Inhibitors EHOMO ELUMO ∆E I A χ η ∆N
Pronated L-H
DFT/B3LYP -8.1177 -4.6654 -3.4523 8.1177 4.6654 6.3915 1.7262 0.1762
Ab initio MP2 -10.2720 -1.0814 -9.1907 10.2720 1.0814 5.6767 4.5953 0.1440
Pronated L-NH2
DFT/B3LYP -7.0450 -4.6338 -2.4112 7.0450 4.6338 5.8394 1.2056 0.4813
Ab initio MP2 -9.4592 -1.2120 -8.2472 9.4592 1.2120 5.3356 4.1236 0.2018
Pronated L-OCH3
DFT/B3LYP -7.4235 -4.7650 -2.6586 7.4235 4.7650 6.0943 1.3293 0.3407
Ab initio MP2 -9.9305 -1.3124 -8.6181 9.9305 1.3124 5.6215 4.3091 0.1600
Pronated L-NO2
DFT/B3LYP -8.4192 -5.0341 -3.3851 8.4192 5.0341 6.7267 1.6925 0.0807
Ab initio MP2 -10.4484 -1.4066 -9.0418 10.4484 1.4066 5.9275 4.5209 0.1186

Theoretical values of Fe = 7 eV and Fe = 0 eV can be used
to calculate the amount of electron transfer from organic in-
hibitors to Fe metal surfaces. The inhibition efficiency value
obtained from the electron donation of organic inhibitors to Fe
metal coincides with the electron transfer value [37]. Organic

inhibitors’ ability to give electrons can do so to mild steel’s sur-
face (Fe 110). According to Table 2-5, the values for electron
transfer are as follows: L-NH2 > L-OCH3 > L-H > L-NO2.
Table 3 shows that the greatest electron transfer value in L-
NH2 was measured at 0.3107 eV using the MP2/6-311++G

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Figure 2: HOMO, LUMO orbitals, MEP and ESP of the studied molecules

(d,p) technique. These findings provide credence to the idea
that organic inhibitors can bind to metal surfaces during elec-
tron donor-acceptor interactions. L-NH2 is therefore expected
to be the best corrosion inhibitor.

The HOMO, LUMO, ESP, and MEP molecular orbital co-
efficients can represent the region around a molecule, and the
electron probability density can provide information about the
size and electrophilicity of the molecule [38]. Figure 2 illus-
trates the visualization of HOMO, LUMO, ESP, and MEP us-
ing the DFT/6-311++G (d,p) approach to describe the mecha-
nism of adsorption on metal surfaces. In order to identify the
reactive side of a molecule, ESP visualization offers a visual
way for comprehending regions that have higher electron den-
sity than other regions. In ESP, the color red denotes the highest
negative electrostatic potential, blue denotes the most positive

electrostatic potential, and green denotes zero electrostatic po-
tential [15]. Red, orange, yellow, green, and blue are in ascend-
ing order of electrical potential [31]. On the oxygen atom of
the lawstone carbonyl in the organic inhibitor L-NH2, there is
a yellow hue. It is possible that oxygen atoms will get up on
the surface of the metal Fe (110) by adsorptive means. How-
ever, the Fukui function is a more accurate way to assess the
electron density of the area of the molecule that is exposed to
electrophilic or nucleophilic attack [39].

Fukui function was proposed by Parr and Yang 1984 [40] as
a measure of local reactivity indicating the presence of reactive
site regions in molecules such as nucleophilic and electrophilic
attack [41]. The preferred site for nucleophilic attack is the
atom in a molecule that has the maximum functional value (f+)
due to its association with ELUMO.

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Table 6: Fukui Functional analysis of L-H, L-NH2, L-OCH3, PP-NO2 molecules

L-H N- N N+ f+ f-
C1 -0.3892 -0.3764 -0.3521 0.0242 0.0129
C2 -0.3095 -0.2896 -0.2386 0.051 0.0199
C3 0.1960 0.2655 0.3007 0.0415 0.0695
C4 0.2357 0.1893 0.2046 0.0153 -0.0464
C5 0.3801 0.3155 0.3413 0.0258 -0.0645
C6 0.1601 0.2399 0.2834 0.0435 0.0798
C7 -0.7657 -0.6214 -0.5695 0.0518 0.1443
C8 0.3974 0.4442 0.5449 0.1007 0.0467
C9 0.0173 0.0293 0.0270 -0.0023 0.0119

C10 -0.8073 -0.7433 -0.7462 -0.0030 0.0641
O11 -0.3682 -0.2058 -0.1222 0.0836 0.1624
O12 -0.3918 -0.2495 -0.1551 0.0944 0.1422
O13 -0.2239 -0.1801 -0.0594 0.1207 0.0437

L-NH2 N- N N+ f+ f-
C1 -0.3939 -0.3661 -0.3428 0.0232 0.0278
C2 -0.3352 -0.3209 -0.3015 0.0194 0.0144
C3 0.1255 0.2094 0.2422 0.0329 0.0839
C4 0.1674 0.1023 0.1057 0.0033 -0.0651
C5 0.7316 0.7209 0.7438 0.0229 -0.0107
C6 0.2215 0.2871 0.3259 0.0388 0.0656
C7 -1.0085 -0.8464 -0.8297 0.0167 0.1621
C8 0.6826 0.6309 0.6519 0.0210 -0.0517
C9 -0.0923 -0.0581 0.0037 0.0618 0.0342

C10 -0.7777 -0.7120 -0.7230 -0.0110 0.0657
O11 -0.3733 -0.2305 -0.1309 0.0996 0.1428
O12 -0.4217 -0.2731 -0.2040 0.0692 0.1486
O13 -0.2321 -0.1923 -0.0572 0.1351 0.0398
N14 -0.5461 -0.4994 -0.3365 0.1629 0.0467

L-OCH3 N- N N+ f+ f-
C1 -0.3773 -0.3638 -0.3401 0.0237 0.0135
C2 -0.4298 -0.4051 -0.3838 0.0213 0.0247
C3 0.1725 0.2412 0.2745 0.0334 0.0687
C4 0.3175 0.2375 0.2323 -0.0052 -0.0800
C5 0.5314 0.4988 0.4992 0.0004 -0.0327
C6 0.1279 0.1853 0.2101 0.0247 0.0574
C7 -0.2970 -0.1380 -0.0629 0.0751 0.1590
C8 0.1008 0.1620 0.2823 0.1202 0.0612
C9 -0.1741 -0.1835 -0.1872 -0.0037 -0.0093

C10 -0.5862 -0.5174 -0.5504 -0.0330 0.0688
O11 -0.3681 -0.2174 -0.1288 0.0886 0.1507
O12 -0.3942 -0.2484 -0.1674 0.0810 0.1458
O13 -0.2453 -0.1946 -0.0523 0.1423 0.0507
O14 -0.3666 -0.3370 -0.2289 0.1081 0.0296
C15 -0.2889 -0.2944 -0.3132 -0.0188 -0.0056

L-NO2 N- N N+ f+ f-
C1 0.3589 -0.3603 -0.3591 0.0012 -0.7192
C2 -0.3791 -0.3404 -0.2778 0.0626 0.0386
C3 0.3035 0.3356 0.3809 0.0453 0.0321
C4 0.3187 0.2703 0.2703 0.0000 -0.0484
C5 0.4743 0.4862 0.5675 0.0814 0.0118
C6 0.1983 0.2693 0.3215 0.0521 0.0711
C7 -0.6848 -0.6217 -0.5946 0.0271 0.0631
C8 0.8653 0.8424 0.8908 0.0484 -0.0229

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C9 -0.3609 -0.2941 -0.2849 0.0092 0.0667
C10 -0.9140 -0.8509 -0.8439 0.0070 0.0631
O11 -0.3236 -0.1723 -0.0865 0.0858 0.1513
O12 -0.2651 -0.1732 -0.0992 0.0740 0.0919
O13 -0.2064 -0.1374 -0.0504 0.0870 0.0690
N14 -0.5459 -0.5019 -0.4841 0.0178 0.0440
O15 0.0364 0.1259 0.2000 0.0741 0.0895
O16 -0.0538 0.0282 0.0892 0.0611 0.0819

Figure 3: Adsorption of organic inhibitors (L-H, L-NH2, L-OCH3, L-NO2) on ferrous metal surfaces in the MC
Fe(110)/inhibitor/100H2O system

Table 7: Adsorption energy of organic inhibitors (L-H, L-NH2, L-OCH3, L-NO2) Fe(110)/inhibitor/100H2O system using MC
simulation

Systems Adsorption energy of inhibitors kcal.mol−1 Adsorption energy of water kcal.mol−1

Neutral Inhibitor
Fe(110)/L-H /100H2O -129.5897925 -13.84984664
Fe(110)/L-NH2 /100H2O -143.4672645 -14.48869095
Fe(110)/L-OCH3 /100H2O -142.3615059 -13.74108729
Fe(110)/ L-NO2 /100H2O -113.8560443 -12.27065388
Protonated Inhibitor
Fe(110)/L-H /100H2O -134.9297789 -13.26018364
Fe(110)/L-NH2 /100H2O -140.5591996 -12.53631498
Fe(110)/L-OCH3 /100H2O -139.2186163 -12.76122573
Fe(110)/ L-NO2 /100H2O -88.50163792 -12.41283883

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The preferred area for electrophilic attack is the atom in the
molecule that has the maximum value of the Fukui function (f-)
because it is associated with EHOMO [42]. The value of f- in-
dicates the ability of an atom to donate electrons to the empty
d orbitals of metal Fe (110) [8]. Table 7 using the DFT/6-
311++G (d,p) method shows that the maximum f+ value of
organic inhibitors L-H on atoms (C8, O12, O13), L-NH2 on
atoms (O11, O13, N14), L- OCH3 on atoms (C8, O13, O14),
L-NO2 on atoms (O11, O13, O15). The atom acts as an elec-
tron acceptor because of the back-donation from the Fe metal
surface [8]. The maximum f- values of organic inhibitors L-
H, L-NH2 and L-OCH3 are found on atoms (C7, O11, O12),
L-NO2 on atoms (O11, O12, N14), respectively. Each organic
inhibitor on the O11 and O12 atoms tends to donate electrons
to the Fe (110) surface so as to form coordinate bonds [43-44].

The most effective way for characterizing the interaction be-
tween substrate and adsorbate is the MC simulation approach.
The lowest desired adsorption energy arrangement for the ad-
sorbate component on the Fe(110) surface can be found using
MC simulation [45]. Figure 3 shows the most stable adsorption
energy configuration of each lawsone derivatives under the con-
ditions of 100 water molecules and the Fe (110) surface. Un-
derstanding the nature of the adsorption process can be aided by
measuring the distance between the atoms in organic inhibitors
and the surfaces of Fe metal. The van der Waals force is re-
garded as being the primary interaction in chemical adsorption
(chemissorption) if the value of this distance is less than 3.5.
These results prove that the organic inhibitor L-NH2 has a dis-
tance between oxygen atoms in O1 of 3.256 Å, O2 of 3.132 Å
and O3 of 3.379 Å and to the surface of Fe (110). The carbonyl
(C=O) and hydroxyl (O-H) atoms can donate electrons to the Fe
(110) surface to form complex compounds. Since more oxygen
atoms contribute as electron donors to the Fe (110) metal sur-
face, the visualization findings of the ESP and Fukui functions
confirm this conclusion. In a MC simulation, the lowest energy
system across all systems is sought after [46]. The adsorption
energy is linked to the energy generated while the relaxed ad-
sorbate is adsorbed on the substrate [47, 48]. Table 7 shows that
the highest negative adsorption value for the organic inhibitor
L-NH2 is -142.3615 kcal/mol. This is caused by the interaction
between the mesomeric effect and the NH2 substituent, which
serves as an electron donor and facilitates the transfer of elec-
trons to the vacant Fe (110) orbital. In order to create stable co-
ordination bonds, L-NH2 possesses a lone pair of electrons on
the oxygen and nitrogen atoms. In order to create the most sta-
ble adsorption layer and shield mild steel from corrosion attack,
L-NH2 is therefore more likely to be adsorbed on the surface of
Fe (110) [49, 50].

4. Conclusion

The effect of substituents (NH2, OCH3, NO2) to the law-
sone structure was studied as a corrosion inhibitor in mild steel
using quantum chemical calculations and MC simulations. It is
possible to predict quantum chemical characteristics from the
structure of corrosion inhibitors. A contribution of electrons to
the surface of mild steel metal can be demonstrated by the large

value of EHOMO and electron transfer from quantum chem-
ical parameters, allowing for the prediction of an increase in
inhibitory efficiency. In comparison to L-H, L-OCH3, and L-
NO2 in a neutral or protonated state, L-NH2 can be projected to
be the best inhibitor based on all the tests that have been per-
formed.

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