Article Type : Research Article
Authors : Ang-yang Yu
Keywords : Physics; Molecular reaction dynamics; Theoretical chemistry; Alloying effects
I engage into the research of theoretical chemistry and condensed physics based on first-principles. My research directions cover a wide range among physics, chemistry, as well as materials science. To list a few representative research interests: molecular spectra; chemical kinetics; molecular excited states; molecular reaction dynamics and Engineering alloy design.
During the last few years, I received some invitations
for delivering a speech regarding my research work in science. Additionally,
there are many concerns about my personal profile both in the internet and in
some academic institutions. Therefore, it seems necessary to write a review
about my personal experience and my research work in science at this particular
times.
I was major in applied physics at Dalian University of
Technology (DUT), Department of physics (China) during the time 1999.9-2003.7,
and received my bachelor’s degree in 2003. Like someone else who studied
physics, I learnt theoretical mechanics, electrodynamics. Thermodynamics and
statistical physics, as well as quantum mechanics in sophomore. In junior and
senior, I noticed some research directions or research topics through listening
to some reports and speech made by the faculties in the physics department. For
example, quark confinement in theoretical physics by one of my teachers, who
had taught us quantum physics. The experimental search for free quark has no
new findings since the quark model was put forward in the year of 1964. Quark
confinement is still the fore-frontier problem in modern physics since the
quantum chromodynamics (QCD) cannot prove quark confinement directly.
Non-topological soliton model is very successful in describing the static
properties of hadrons [1]. Beginning with the soliton model, a soliton solution
has been obtained. The calculated results show that the mass of quark is zero
inside hadron, whereas the mass of quark outside the boundary of hadron is much
larger than the mass of quark inside hadron. Therefore, much more energy is
needed to generate a quark outside hadron than the energy needed to generate a
quark inside hadron, which serves as a good explanation of quark confinement
[2]. I had also touched upon
the field of molecular reaction dynamics through a seminar report made by my senior
sister apprentice. Later on, the physics department organized a visit to the
State Key Laboratory of molecular reaction dynamics in Dalian Institute of
Chemical Physics, where there is the universal crossed molecular beam apparatus
as is shown in Figure 1, which gave me a deep impression and set the foundation
for writing a review regarding some important experimental techniques in
molecular reaction dynamics [3]. This review has introduced some representative
crossed molecular beam apparatus in molecular reaction dynamics. A history of
crossed molecular beam equipment is reviewed in this paper. The detectors of
both the universal crossed molecular beam machine and Hydrogen atom Rydberg
tagging apparatus have been discussed. Other types of crossed molecular beam
instruments have also been reviewed. Each experimental apparatus makes a
compromise among the resolution, sensibility and universality. Hopefully, new
types of experimental techniques can emerge and contribute the development of
molecular reaction dynamics and relevant research fields. I had learned a course called plasma
physics in my junior. Although there are famous advanced Tokomak apparatus in
the experiment [4]. More attention is paid to the theoretical side, including
sheath [5,6]
and positive column [7]. Positive column of direct current (DC) glow discharge
is primarily used in the field of plasma material surface modification. In this
kinetic modeling of a hydrogen glow discharge positive column, electron energy
distribution function (EEDF) is found to depart from Maxwell distribution
obviously. The distribution tail moves to higher energy when the ratio between
electric field E and density of neutral species N (E/N) increases and the tail
moves towards higher energy if hydrogen atom proportion increases at the same
E/N. It is shown that electronic temperature rises with the increase of E/N.
Additionally, the dissociation ratio percentage of H2 augments with the rise of
E/N. My junior and senior were
mainly concerned with semiconductor physics. My graduation design is concerned
with GaN semiconductor crystal growth using Monte Carlo method. I had written a
FORTRAN code to simulate the growth process of GaN crystal. As an important
third-generation semiconductor material, GaN can also be investigated by
First-principles [8,9]. During the period of my graduation design, one of my
senior fellow apprentices advised me to enter into DICP to perform my research
work. With some interests in the chemical reactions at molecular level, namely,
molecular reaction dynamics, I entered the examination of national research
students after some prior inquires and preparations for the exam and was
enrolled by Dalian Institute of Chemical Physics, Chinese Academy of Sciences
in 2003.
I continued my research work at State Key Laboratory
of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics (DICP) and
obtained my master’s degree in 2006. My diploma at that time has been presented
below. There are two main
research interests for me from 2003.9 to 2006.7. The former is the calculations
of molecular spectra using quantum physics method. A modified three dimensional
discrete variable representation (MDVR3D) program which could be used to
calculate the bound states vibration spectrum of some tri-atomic molecules is
developed [10,11]. Both the three dimensional discrete variable representation
(DVR3D) program and the MDVR3D program are used to calculate the vibration
energy levels of the isotopic species of hydrogen sulfide (H232S, H233S, H234S,
D232S, D233S, D234S, T232S, T233S, T234S). This work forms the basis for
dealing with the rotational spectrum calculations and presents the first
theoretical results for D233S, T232S, T233S and T234S. The
latter is the investigation of molecular reaction dynamics using classical
trajectory method. The quasi-classical trajectory (QCT) calculation for the
reaction O (1D) +CH4 was performed based on a new London-Eyring-Polanyi-Sato
(LEPS) potential energy surface (PES). Attention of this work has been attached
to the OH+CH3 product channel. Product angular distribution has been studied,
which are in excellent agreement with previous experimental results. It is
found that there is a forward scattered peak and a backward scattered peak for
the OH product relative to the O(1D) beam direction at the collision energy of
6.8Kcal/mol [12].
After graduation from DICP, I worked as a teaching
faculty in Liaoning University of Petroleum and Chemical Technology (LNPU)
between the year of 2006 and 2011, when scientific research was still an
important part of my daily work as the college attaches particular importance
to published papers in all kinds of scientific journals. My first published
work in this university is a review regarding the geometric phase effect [13].
Some theoretical approaches, including the geometric phase effect, were
reviewed because there are many breakthroughs and progresses about the theory
of conical intersection in the past years. Some results concerned with the
geometric phase effect in the reaction dynamics had been demonstrated and there
were also explanations for those intriguing results in this review. It is known
that conical intersection could influence nuclear dynamics through the
geometric phase effects. The Schrodinger equation acquires a vector potential
term in the adiabatic representation. Based upon this expression and the
theoretical treatment of the nuclear Schrodinger equation in the diabatic
representation, a new equation is derived which incorporates both the geometric
phase effects and other non-adiabatic factors [14]. As
a teaching faculty in LNPU, I had taught some college experiments to the
freshman and sophomore, for example, the resistance measurement by Wheatstone
bridge. In view of its importance in measuring resistance, Wheatstone bridge
has played an important role in resistance measurement. My work aims to improve
the measured accuracy and precision of self-organized bridge and Box Bridge, as
is shown in the figure below, with the left denoting the box bridge and the
right standing for the self-organized bridge. The
experimental results obtained thus far have reached an unprecedented high level
for high-precision measurement. To the largest extent for a specific
resistance, both the self-organized bridge and Box Bridge have gained the most
consistent measured value [15].
During the period 2011.8-2014.7, I performed my
research work at Institute of Theoretical Chemistry, Jilin University,
Changchun, Jilin province, and obtained my PhD’s. Degree in 2014 at Jilin
University of China. The main research work during this time can be summarized
as follows:
It is well-known that controlling the chemical
reactions of atmospheric pollutants is a feasible way to solve the
environmental pollution. These atmospheric pollutants are mainly produced from
radical-molecule or radical-radical reactions. Since these type of reactions
are fast and complicated in the microscopic level, it is very difficult to
measure experimentally. Therefore, theoretical chemistry methods are needed to
investigate this type of reaction. Based on the computed potential energy
surface, it is feasible to predict the possible reaction products and best
reaction channel, as well as the dependence of reaction rate constants with
temperature. Additionally, the calculation of reaction products’ ratio in
atmosphere chemistry and combustion can serve as a theoretical guide for future
experimental research [16-18].
The ground and low-lying excited states of some
organic molecules have been studied theoretically. The calculated vertical
excitation energies and vertical ionization potentials are compared with
available experimental values. In addition, the vertical electron affinity and
the adiabatic electron affinity are calculated either [19-22].
As some applications in the related field of chemical
and material science, this work aims to presentate and characterize some new
chemical materials. A new series of compounds Al3-X (X=F, LiF2, BeF3, BF4),
consisting of aluminum trimer and fluorine atom or its superhalogens (LiF2,
BeF3, BF4), have been theoretically designed. The best interaction orientation
between Al3 cluster and fluorine atom or its superhalogens (LiF2, BeF3, and
BF4) has been identified and binding energies of this type of compounds have
also been calculated. HOMO-LUMO energy gap of these compounds has been used to
test the stability of these compounds. Additionally, aromaticity of this type
of compounds has been confirmed.
After obtaining my Ph.D. degree at Jilin University in
China, I was awarded a Post doctor’s Fellowship to investigate titanium alloys'
oxidation at Institute of Metal Research, Chinese Academy of Sciences from
2014.12 to 2016.06. My Post doctor’s research performed in Chinese Academy of
Sciences can be listed as follows:
First-principles method has been successfully applied
in the condensed state physics. The first-principles method is used to find out
the oxidation properties of titanium alloys. Since the simulation is at the
atomic level, it is possible to f and out some clues of improving the oxidation
resistance of titanium alloys [24,25].
In the realm of materials science, the research of
plastic deformation of metals attaches great importance to stacking fault
energy (SFE). In this paper, we derive the expressions of four types (I1, I2, E
and T2) of basal plane SFEs of hcp-Ti within the framework of the Ising model.
Based on this model, alloying effects on the stacking fault energy (SFE) of
titanium alloys are investigated via first-principles calculations. It is found
that SFE always decreases with addition of alloying elements. The distribution
of lattice parameters of all the studied Ti95X5 has a direct relationship with
alloying element’s atomic radii. Additionally, SFEs decrease linearly with the
solutes concentration increasing in the Ti-based alloys. This work provides
some useful data for new Ti alloys design [26].
My original research dream in materials science is
related with mechanics of materials. In the computational materials studies
during my postdoctoral period, the structural, electronic and mechanical
properties of RuBx(x=1, 2, 3) are investigated by performing ?rst principles
calculations using density functional theory (DFT). The calculated lattice
constants agree well with the available results. The chemical bonding is
interpreted by calculating the electron localization function (ELF). The
covalent Ru-B bond and B-B bond become stronger with the increase of boron’s
concentrations, which can help improve the hardness of RuBx system. Moreover,
RuB has the highest bulk modulus, which means more prominent volume-compression
resistance. RuB2 has a certain elastic anisotropy and RuB3 has the best
toughness [27].
Universal Crossed
Beam Molecular Reaction Dynamics Machine
My research work had been guided by many eminent
professors, who gave inspirations in my research. I had acted as a Visiting
Scholar from 2016.10 to 2018.11 in Ludong University, where I performed some
scientific research work in molecular physics and physical chemistry. Some
topics are listed below:
It is well-known that the Configuration
self-consistent field (MCSCF) method ismost suitable for the calculation of the
potential energy curves or potential energy surfaces. In this work, this method
is adopted for the investigation of 4?- state in the diatomic BX (X=He, Ne, Ar,
Kr), as is exhibited in those figures below. The
computed energies of potential energy curves (PEC) for the B-X (X=He, Ne, Ar,
Kr) series are ?tted to analytical potential energy function (APEF) using
nine-order Murrell-Sorbie function. Compared with previous results, more
accurate spectroscopic constants have been obtained. To describe the
dissociation behavior correctly, the dissociation energy and equilibrium
distance of the B-X (X=He, Ne, Ar, Kr) series have also been determined.
Additionally, some vibration energy levels of this electronic state have been
predicted, and they are in excellent agreement with experimental data.
Feshbach resonances do not restricted to small
reactive systems such as F+H2 and IHI [28]. It can be found in many reactive
systems. In this work, the concept of the partial potential energy surface
(PPES) is introduced. It is shown that the dynamic Eyring Lake explains very
well the existence of reactive resonances in elementary chemical reactions.
Particularly, the PPESs of the Cl+CH3CH2Br and Cl+CH3CH2CH2Br systems including
the minimum energy path (MEP) and the vibration potential energy curves were
constructed using quantum chemistry methods. Based on the constructed PPESs,
the scattering resonance states of these reactions can be expected and the
resonance state lifetime was estimated [29].
Substitution effects are common phenomena in
natural science. To a large extent, substitution of methane with chlorine will
influence the mechanism and kinetics of the reactions between chloromethane and
atomic chlorine [30]. In the area of molecular spectra, vibration energy levels
of hydrogen sulfide substituted by isotopic elements will shift. Additionally,
alloying element’s substitution in titanium alloy can improve oxidation
resistance in the realm of material sciences. In my recent work, the geometry, electronic
structure, and infrared spectra (IR) of meso-tetra-substituted porphyrin have
been investigated. The substitution of pyridyl for phenyl in
meso-tetra-substituted porphyrins can result into the reduction of molecular
size, including the molecular diameter, as well as the size of the central ring
of porphin. It has also been found that the molecular orbital energies of T
3PyP are smaller than the counterparts of TPP whereas there is almost no change
in the HOMO–LOMO gap. Additionally, the infrared spectrum of TPP and T3PyP has
been compared in order to determine whether there is a red shift or a blue
shift [31]. In recent days, I
also reflect upon the source of innovation and the art of discovery in physics
[32]. Simply because many breakthroughs in the history of physics originate
from the raising of scientific questions and promote the true progress of
science and technology. Physicists not only have the courage to innovate and
face difficulties, but also can use the correct research methods to show the
art of scientific discovery to the world.
My research experience dates from the year of 2003,
when I was performing my graduation design in Dalian University of Technology
(DUT). As the first author or corresponding author, I has published more than
30 scientific articles in many international journals. The intention of this
article is not only to introduce my personal experience, but also to explain my
research profiles during the past several years. The topics of my research
belong to physical chemistry and chemical physics.
I
want to express my thanks to my parents, my relatives and my friends for
putting up with me.