A first-principles study of propanol adsorption on Monolayer
Molybdenum Diselenide (MoSe2)
Luong Thi Theu1, Tran Thi Nhan2, Tran Quang Huy3, Van An Dinh1,4
1

Institute of Applied Technology, Thu Dau Mot University, Binh Duong, Vietnam
2

Faculty of Fundamental Sciences, Hnoi University of Industry, Hanoi, Vietnam
3
4

Faculty of Physics, Hanoi Pedagogical University 2, Hanoi, Vietnam

Department of Precision Engineering, Graduate School of Engineering, Osaka
University, Osaka, Japan

ABSTRACTS
It is desirable to seek new sensors capable of detecting VOCs at low concentrations in the early
stages of cancer. Because of their high surface area to volume ratio, 2D TMDs are predicted to
be appealing materials for gas sensitive sensors. In this work, we investigate the adsorption
mechanism of propanol gas on the surface of monolayer MoSe2 by the quantum simulation
method. The images of the potential energy surfaces for configuration of adsorbate on MoSe2
surface were investigated using the Computational DFT-based Nanoscope tool to explore the
most stable configurations and diffusion possibilities. The optPBE-wdW functional was used for
discussing the adsorption mechanism, electronic structure, and charge transfer. It is found that by
using optPBE-vdW functional, the propanol-adsorbed MoSe2 is physisorbed with a pretty high
energy of 436 meV, which indicates that MoSe2 is considerably sensitive with this gas. The
charge transfer between the substrate and VOCs was also addressed.
Keywords: Adsorption, VOCs, propanol, monolayer MoSe2, DFT.

Nghiên cứu nguyên lý ban đầu của hấp phụ khí propanol lên đơn lớp
Molybdenum Diselenide (MoSe2)
Luong Thi Theu1, Tran Thi Nhan2, Tran Quang Huy3, Van An Dinh1,4
1

Institute of Applied Technology, Thu Dau Mot University, Binh Duong, Vietnam
2

Faculty of Fundamental Sciences, Hnoi University of Industry, Hanoi, Vietnam
3
4

Faculty of Physics, Hanoi Pedagogical University 2, Hanoi, Vietnam

Department of Precision Engineering, Graduate School of Engineering, Osaka
University, Osaka, Japan
56


TĨM TẮT
Chúng ta mong muốn tìm ra các cảm biến mới có khả năng phát hiện hợp chất hữu cơ dễ bay
hơi ở nồng độ thấp trong giai đoạn ung thư sớm. Do tỷ lệ diện tích bề mặt trên thể tích cao, vật
liệu kim loại chuyển tiếp dichalcogenides hai chiều được dự đoán là vật liệu hấp dẫn cho các
cảm biến nhạy khí. Trong bài báo này, chúng tơi nghiên cứu cơ chế hấp phụ của khí propanol
trên bề mặt của MoSe2 đơn lớp bằng phương pháp mô phỏng lượng tử. Hình ảnh thế năng lượng
bề mặt cho cấu hình của chất hấp phụ trên bề mặt MoSe2 đã được khảo sát bằng cách sử dụng
công cụ Nanoscope dựa trên tính tốn lý thuyết hàm mật độ để khám phá cấu hình ổn định nhất
và khả năng khuếch tán. Phiếm hàm optPBE-wdW được sử dụng để thảo luận về cơ chế hấp phụ,
cấu trúc điện tử và sự truyền điện tích. Bằng cách sử dụng phiếm hàm optPBE-vdW chúng tôi
thấy rằng, hấp phụ propanol trên MoSe2 là hấp phụ vật lý với năng lượng khá cao khoảng 436

meV, điều này cho thấy MoSe2 rất nhạy với khí này. Sự dịch chuyển điện tích giữa chất nền và
khí cũng được thảo luận.
Từ khóa: Hấp phụ, hợp chất hữu cơ bay hơi, propanol, đơn lớp MoSe2, lý thuyết hàm mật độ.

1. Introduction
Volatile organic compounds (VOCs), which are found in the breath of people with earlystage cancer, are considered as new cancer biomarkers for diagnostic purposes [1-4]. It has been
shown that early diagnosis increases the chances of survival in patients with various types of
cancer [5,6]. Breath analysis might provide the foundation of a non-invasive technique for early
cancer detection by gas sensitive sensors.
Traditional semiconductor metal oxide based gas sensors have good selectivity and
sensitivity [7], but they generally require high operating temperatures, which lead in high power
consumption and inducing deviation in results. 2D transition metal dichalcogenides (TMDs)
have attracted a lot of interest as a chemical sensing device alternative to traditional metal
oxides. Because of its outstanding semiconductor characteristics, this material family has been
found with applications in a variety of disciplines including photocatalysis, optoelectronics,
electronics, spintronics, and gas sensors [8-12]. Among the 2D TMD materials, monolayer (ML)
MoSe2 displays appealing electronic properties including high surface-to-volume ratio, stability,
high conductivity, and layered structure, and the capacity to adjust the number of layers [13-15].
57


Therefore, MoSe2 is expected to be a promising semiconductor option for the design and
manufacturing of high-performance gas sensing devices [16-20].
In the present study, by first principle simulation method, we explore the mechanism,
structural and electronic properties of MoSe2 monolayer adsorbed on the surface of propanol gas
using the non-empirical van der Waals (vdW) density functional. The most favored configuration
of the gas-MoSe2 adsorption system was explored by optimizing the geometric structure and
computing the interaction energy with the Computational DFT based Nanoscope tool [21-23].
The adsorption energy profile was calculated in detail with the optPBE-vdW functional to
evaluate the propanol sensitivity of MoSe2. In addition, the influence of gas adsorption on the

electronic structure, as well as the charge transfer mechanism between the substrate and the gas
molecule, are carefully considered with the appropriate optPBE-vdW functional.

2. Computational Method
The adsorption mechanism of propanol toward the surface of a MoSe2 4x4 supercell was
studied theoretically using Density Functional Theory (DFT) [24-26]. Ab initio calculation
simulation was done on High Performance Computers using the density functionals approach
implemented in Vienna Ab initio Simulation Package (VASP) [27, 28]. The van der Waals
interaction is accounted for by using the optPBE-vdW functional [29, 30]. Automatic scanning
using a Computational DFT-based Nanoscope [21-23] was used to find the most optimal
adsorption geometries of the adsorbate on the MoSe2 substrate, and the adsorption energy
profile. A cutoff energy of 500 eV for the plane-wave basis set and a 4x4x1 Gamma-centered kpoint mesh corresponding to the 4x4 super-cell were utilized. A vacuum thickness of 20 Å was
applied to eliminate the interaction between layers. The structures were all thoroughly relaxed
until the maximum residual Hellmann-Feynman force acting on each atom was less than 0.01
eV/Å.
The adsorption energy Ead is calculated by the following equation:
Ead = Egas+sub − ( Egas + Esub ) ,

(1)

where Egas+sub, Egas, and Esub are the total energies of the gas-MoSe2 system, isolated gas
molecule, and isolated MoSe2, respectively. Bader charge analysis was used to estimate the
Charge Differential Density (CDD) of the most favorable adsorption configuration. The charge
58


density difference is calculated using the equation  =  AB −  A −  B [31], in which ρAB is the
total charge of the system, ρA and ρB are the charges are two separate systems. The visualization
using in this paper is VESTA, which was developed by K. Momma and F. Izumi [32].


3. Results and Discussions
3.1. Geometrical structure of propanol and the stable position of adsorption
system propanol-MoSe2
Propanol is an organic compound with the molecular formula CH3CH2CH2OH that belongs
to the alcohol functional group. Figure 1 illustrates the molecular structure of propanol, with
carbon, hydrogen, and oxygen atoms represented by the brown, light pink, and red spheres,
respectively. Propanol concentrations in the breath of patients with lung, liver, and stomach
cancers have been reported [1, 2, 4], that play a critical role in early cancer detection.

Figure 1. Molecular structure of propanol

Figure 2. Top (a) and side (b) views of propanol adsorption on MoSe2. The Se and Mo atoms are
represented by the green and purple spheres, respectively.
59


By carefully optimizing the geometry structures of the gas-MoSe2 adsorption systems using
the Nanocope tool, the most stable configuration of the propanol-MoSe2 adsorption systems was
explored, as shown in Figure 2. This tool has been used to simulate the adsorption of organic
gases on other 2D materials, such as brophene [22] and silicene [23]. It is discovered that the
most preferred adsorption site is the gas oriented parallel to the substrate, approximately 2.7 Å
from the material's surface to the gas's lowest atomic position. When the structures of gas and
material were compared before and after adsorption, the bond angles and bond lengths showed
very little variations in both. This suggests that MoSe2 is a highly stable sensor material.

3.2. Binding potential, adsorption energy profile of propanol onto MoSe2
The stable positions of adsorbent can be determined by the minima of the potential energy
surface (PES). When PES equals zero, the adsorption system is in the most equilibrium state.
Because of the periodicity in the ML MoSe2 lattice structure, it is only necessary to compute PES
of unitcell instead of supercell. Figure 3 shows the potential energy surface per unitcell of

propanol gas on ML MoSe2. The color gradient represents the PES value, with brighter colors
exhibiting a higher PES values and vice versa. According to this convention, the blue and black
regions correspond to favorable adsorption areas. Unfavorable adsorption areas are represented
by the yellow and orange colors. Diffusion allows gas molecules to move between adsorption
regions. Because the minimum energy difference between the propanol adsorption regions is 15
meV, the adsorption regions will be linked, indicating that MoSe2 is quite sensitive to this gas.

Figure 3. The 3D projected Potential Energy Surface for the adsorption of propanol on the surface of
MoSe2.
60


Table 1 shows the adsorption characteristics of propanol on MoSe2 with the optPBE-vdW
functional. The optimal adsorption distance dz (dc) is the distance from the lowest atom (center
of mass –COM) of the gas molecule to the surface of MoSe2. It was discovered that the
propanol-adsorbed MoSe2 is physisorbed with a pretty high energy of 436 meV. The adsorption
distance between the lowest atom and the substrate is 2.631 Å, the response length l is 9.867 Å,
and the recovery time τ is quite small, 20 microseconds. According to the findings, MoSe2 is
extremely sensitive to propanol vapor.

Table 1. Adsorption energy (Ead), equilibrium height of the lowest atom (dc), equilibrium height of the
massed center (dz), response length (l), and recovery time (τ) for the adsorption of propanol on MoSe2
using optPBE-vdW functional.
Molecule

Propanol

Adsorption
properties


optPBEvdW

Ead (meV)

-436

dz(Å)

2.631

dc(Å)

3.513

l(Å)

9.867

τ (µs)

20.34

3.3. Electronic band structure and charge transfer of propanol gas on MoSe2
monolayer
3.3.1. Electronic band structure
To investigate the nature of propanol adsorption on MoSe2, we computed the band dispersion
and density of states along high symmetry k-points. We observed that ML MoSe2 exhibits a
direct band gap involved to the Brillouin zones' K-K shift with the band gap value of
approximately 1.418 eV, in good agreement with previous calculations [33, 34]. Based on the
calculation results shown in Figure 4, the electronic band structure of MoSe2 shows a decrease in

the band gap by about 7.8 meV. Decreasing a band gap might lead to the increasing of electrical
conductivity, which implies the possibility of detecting VOCs by monitoring the conductance of
MoSe2 upon exposure to a breath containing VOCs.

61


Figure 4. Band structures and density of states (DOS) of propanol on MoSe2 (optPBE-vdW functional).
The dashed lines represent Fermi level. DOS is in units of state/eV.

3.3.2. Charge transfer mechanism
Bader charge analysis was used to determine charge transfer. The amount and direction of
charge transfer may be determined by comparing the charge before and after adsorption of a
VOC molecule. After adsorption, the positive sign indicates electron accumulation, which is
represented by the yellow color, whereas the negative sign shows electron depletion, which is
represented by the blue hue.

Figure 5. Top (a) and side (b) views of charge density difference (CDD) by the adsorption of propanol on
monolayer MoSe2.

We discovered that, propanol acts as an electron acceptor from substrate. The amount of
charge transferred about 0.4e are higher by far than its chemical-adsorption on single-layer
62


stanane in previous work[35]. The donated charge is believed to change the resistivity of the
adsorbent, MoSe2, making it a selective and sensitive material to propanol gas.

4. Conclusion
We have investigated the interaction between freestanding ML MoSe2 and propanol gas by

the quantum simulation based on the Density functional theory with the use of the optPBE-vdW
functional. The picture of PES, favorable adsorption configuration, electronic structure, and
charge transfer were computed. Upon propanol gas adsorption, a decrease in the band gap by
about 7.8 meV appears in the electronic structure of MoSe2, resulting in changeable conductivity.
It is also found the charge transfer of 0.4 electrons between VOC and material, suggesting a
possibility of the use of MoSe2 material in the sensing devices, especially in VOC sensors.

References
[1] Z. Jia, A. Patra, V.K. Kutty, T. Venkatesan, (2019), Critical review of volatile organic
compound analysis in breath and in vitro cell culture for detection of lung cancer, Metabolites,
9, 1.
[2] M. Hakim, Y.Y. Broza, O. Barash, N. Peled, M. Phillips, A. Amann, H. Haick, (2012),
Volatile organic compounds of lung cancer and possible biochemical pathways, Chem. Rev,
112, 5949–5966.
[3] H. Amal, D.Y. Shi, R. Ionescu, W. Zhang, Q. Hua, Y. Pan, L. Tao, H. Liu, (2015),
Assessment of ovarian cancer conditions from exhaled breath, Int. J. Cancer, 136, E614.
[4] A. Amann, B. de Lacy Costello, W. Miekisch, J. Schubert, B. Buszewski, J. Pleil, R.
Norman, T. Risby, (2014), The human volatilome: volatile organic compounds (VOCs) in
exhaled breath, skin emanations, urine, feces and saliva, J. Breath Res, 8, 034001.
[5] V. K. Chaturvedi, A. Singh, V. K. Singh, et al, 2018, Cancer nanotechnology: a new
revolution for cancer diagnosis and therapy, Curr Drug Metab, 20, 416.
[6] P. J. Kaboli, A. Rahmat, P. Ismail, et al, (2015), MicroRNA-based therapy and breast cancer:
a comprehensive review of novel therapeutic strategies from diagnosis to treatment, Pharmacol
Res, 97, 104.
[7] S. M. Kanan, O. M. El-Kadri, I. A. Abu-Yousef, M. C. Kanan, (2009), Semiconducting Metal
Oxide Based Sensors for Selective Gas Pollutant Detection, Sensors, 9, 8158.
[8] K. F. Mak, C. Lee, J. Hone, J. Shan, T. F. Heinz, (2010), Atomically thin MoS2: a new directgap semiconductor, Phys. Rev. Lett, 105,136805
[9] A. Splendiani, L. Sun, Y. Zhang, T. Li, J. Kim, C.Y. Chim, G. Galli, F. Wang, (2010),
Emerging photoluminescence in monolayer MoS2, Nano Lett, 10, 1271.
63



[10] Sundaram, R. S.; Engel, M.; Lombardo, A.; Krupke, R.; Ferrari, A. C.; Avouris, P.; Steiner,
M. (2010), Electroluminescence in Single Layer MoS2, Nano Lett, 13, 1416.
[11] D.J. Late, Y.K Huang, B. Liu, J. Acharya, S.N. Shirodkar, J. Luo, C.N.R. Rao, (2013),
Sensing behavior of atomically thin-layered MoS2 transistors, ACS Nano, 7, 4879.
[12] Y. K. Kyung, P. Kyunam, L. Sangyoon, K. Youngjun, J. D. Whang, K. Donghyun, S.
Jeong-Gyu, P. Jusang, K. Hyungjun, Recovery Improvement for Large-Area Tungsten Diselenide
Gas Sensor, ACS Appl. Mater. Interfaces, 2018, 10, 23910.
[13] M. Nayeri, M. Moradinasab, M. Fathipour, (2018), The transport and optical sensing
properties of MoS2, MoSe2, WS2 and WSe2 semiconducting transition metal dichalcogenides.
Semiconductor Science and Technology, 33, 025002.
[14] V. Babar, H. Vovusha, U. Schwingenschlögl, (2019), Density Functional Theory Analysis of
Gas Adsorption on Monolayer and Few Layer Transition Metal Dichalcogenides: Implications
for Sensing, ACS App. Nano Mater, 2, 6076.
[15] R. Roldan, J. A. Silva-Guillen, M. P. Lopez-Sancho, F. Guinea, E. Cappelluti, P. Ordejon,
(2014) Electronic properties of single-layer and multilayer transition metal dichalcogenides MX2
(M = Mo, W and X = S, Se), Ann. Phys, 526, 347.
[16] D.J. Late, T. Doneux, M. Bougouma, (2014), Single-layer MoSe2 based NH3 gas
sensor, App. Phys. Let, 105, 233103.
[17] J. Baek, D. Yin, N. Liu, I. Omkaram, C. Jung, H. Im, S. Kim, (2017), A highly sensitive
chemical gas detecting transistor based on highly crystalline CVD-grown MoSe2 films, Nano
Res, 10, 1861.
[18] W. Ai, L. Kou, X. Hu, Y. Wang, A.V. Krasheninnikov, L. Sun, X. Shen, (2019), Enhanced
Sensitivity of MoSe2 Monolayer for Gas Adsorption Induced by Electric Field,
J. Condens. Matter Phys, 31,445301.
[19] P. Panigrahi, T. Hussain, A. Karton, R. Ahuja, (2019), Elemental substitution of twodimensional transition metal dichalcogenides (MoSe2 and MoTe2): implications for enhanced
gas sensing, ACS sens, 4, 2646.
[20] V. Nagarajan, R. Chandiramouli, (2018), MoSe2 nanosheets for detection of methanol and
ethanol vapors: a DFT study, J. Mol. Graph. Model, 81, 97.

[21] Computational DFT-Based Nanoscope, developed by Van An Dinh, Vietnam Japan
University, 2017.
[22] T. T. Luong, I. Hamada, Y. Morikawa, V. A. Dinh, (2021), Adsorption of toxic gases on
borophene: surface deformation links to chemisorptions, RSC Adv, 11, 18279.
[23] V. O. Vo, T. L. Pham, V. A. Dinh, (2020), Adsorption of Acetone and Toluene on SingleVacancy Silicene by Density Functional Theory Calculations, Mat. Trans, 61,1449.
[24] W. Kohn, L. J. Sham, (1965), Self-consistent equations including exchange and correlation
effects, Phys. Rev, 140, A1133.
[25] P. Hohenberg, W. Kohn, (1964), Inhomogeneous electron gas, Phys. Rev, 136, B864.
[26] D. Vanderbilt, (1990), Soft self-consistent pseudopotentials in a generalized eigenvalue
formalism, Phys. Rev. B, 41, 7892.
64


[27] G. Kresse, (1995), Ab initio molecular dynamics for liquid metals, J. Non. Cryst. Solids,
192, 222.
[28] G. Kresse, J. Hafner, (1994), Ab initio molecular-dynamics simulation of the liquidmetalamorphous- semiconductor transition in germanium, Phys. Rev. B, 49, 14251.
[29] J. Klimeš, D.R. Bowler, A. Michaelides, (2009), Chemical accuracy for the van der Waals
density functional, J. Phys. Condens. Matter, 22, 022201.
[30] Y. Zhang, W. Yang, (1998), Comment on “Generalized gradient approximation made
simple”, Phys. Rev. Lett, 80, 890.
[31] Henkelman group 2017, Code: Bader Charge Analysis.
/>[32] K. Momma, F. Izumi, (2011), VESTA 3 for three-dimensional visualization of crystal,
volumetric and morphology data, J. Appl. Crystallogr, 44, 1272.
[33] S. K. Mahatha, K. D. Patel, K.S. Menon, (2012), Electronic structure investigation of MoS2
and MoSe2 using angle-resolved photoemission spectroscopy and ab initio band structure
studies, J. Condens. Matter Phys, 24, 475504.
[34] Y. Ma, Y. Dai, M. Guo, C. Niu, J. Lu and B. Huang, (2011), Electronic and magnetic
properties of perfect, vacancy-doped, and nonmetal adsorbed MoSe2, MoTe2 and WS2
monolayers, Phys. Chem. Chem. Phys, 13, 15546.
[35] V. Nagarajan, R. Chandiramouli, (2017), Interaction of alcohols on monolayer stanane

nanosheet: a first-principles investigation, App. Sur. Sci, 419, 9.

65