One of the standard approaches to calculate the ground-state properties of strongly correlated electronic systems is to use a Jastrow–Slater wavefunction as a starting point. When considering confined electrons in a two-dimensional parabolic quantum dot, one chooses the Slater determinant to be the ground-state wavefunction of confined independent electrons and then determines the form of the Jastrow correlation factor in a way that incorporates accurately the spatial correlations of the system. One way to choose a quality Jastrow correlation factor is to consider the two-body problem and search the best possible yet simple approximative solution to such a problem. To achieve this goal, we consider the two-body problem of confined electrons interacting with a Coulomb repulsive potential in zero magnetic field and focus on their relative motion. Based on straightforward theoretical considerations, we suggest a simple two-body Jastrow correlation factor that optimizes very well the overall trial energy. We test the quality of the proposed Jastrow correlation factor by comparing the results to exact numerical diagonalization solutions.
One of the standard approaches to calculate the ground-state properties of strongly correlated electronic systems is to use a Jastrow–Slater wavefunction as a starting point. When considering confined electrons in a two-dimensional parabolic quantum dot, one chooses the Slater determinant to be the ground-state wavefunction of confined independent electrons and then determines the form of the Jastrow correlation factor in a way that incorporates accurately the spatial correlations of the system. One way to choose a quality Jastrow correlation factor is to consider the two-body problem and search the best possible yet simple approximative solution to such a problem. To achieve this goal, we consider the two-body problem of confined electrons interacting with a Coulomb repulsive potential in zero magnetic field and focus on their relative motion. Based on straightforward theoretical considerations, we suggest a simple two-body Jastrow correlation factor that optimizes very well the overall trial energy. We test the quality of the proposed Jastrow correlation factor by comparing the results to exact numerical diagonalization solutions.
The ground states of parabolically confined electrons in a quantum dot are studied by both direct numerical diagonalization and quantum Monte Carlo (QMC) methods. We present a simple but accurate variational many-body wave function for the dot in the limit of a weak magnetic field. The wave function has the center-of-mass motion restricted to the lowest-energy state and the electron-electron interaction is taken into account by a Jastrow two-body correlation factor. The optimized wave function has an accuracy very close to the state-of-the-art numerical diagonalization calculations. The results and the computational efficiency indicate that the presented wave function combined with the QMC method suits ideally for studies of large quantum dots.
With the ability to solve the many-body Schrödinger equation accurately, in principle all physics and chemistry could be derived from first principles. However, exact wave functions of realistic and interesting systems are in general unavailable because they are non-deterministic polynomial-hard to compute (Troyer, 2005). This implies that we need to rely on approximations. The variational Monte Carlo (VMC) method is widely used for ground state studies, but requires a trial wave function ansatz which must trade off between efficiency and accuracy. The method also has many common features with machine learning algorithms, and as neural networks have shown impressive power as function approximators, the idea is to use a neural network as the trial wave function guess. For fermionic systems, like electronic structure systems, the wave function needs to obey Fermi-Dirac statistics. This is typically achieved using a Slater determinant. As a neural network hardly can model this feature, our approach is to replace the single-particle functions in the Slater determinant with restricted Boltzmann machines, getting the RBM ansatz. In addition, we add further correlations via so-called Jastrow factors (Drummond, 2004). The de facto standard trial wave function ansatz for electronic structure calculations is the Slater-Jastrow ansatz, which was implemented as a reference. Our primary focus is on closed-shell circular quantum dots, where we compute the ground state energy and electron density of two-dimensional systems with up to 90 electrons and three-dimensional systems with up to 70 electrons. The energy obtained by the RBM ansatz was reasonably close to experimental results, and it gradually became closer as we added more complex correlation factors. For our most complicated Jastrow factor, the energy was found to be lower than the energy provided by the Slater-Jastrow ansatz for small dots, but for larger dots it was slightly higher. However, the one-body density profile reveals that the RBM ansatz gives more distinctly located electrons compared to the Slater-Jastrow ansatz. This can be explained by the way the RBM ansatz models the correlations. From the two-body density profile, we also observe that the repulsive interactions get more significant as we add a Jastrow factor. Based on the electron densities and the energy distribution between kinetic and potential energy, it is certain that the various methods provide different electron configurations. For low-frequency dots, the electron density becomes more localized with an additional radial peak compared to high-frequency dots. This is reminiscent of what is known as Wigner localization (Ghosal, 2007). The computational time consumption was found to be favorable for the RBM ansatz for small systems and the Slater-Jastrow ansatz for large systems. This can be explained by the exploding number of variational parameters in the RBM ansatz as the system sizes increase. The RBM ansatz with Jastrow factors were notably more computationally intensive than the other ansätze, and evidently, there is no reason to use the simplest Jastrow factor when more complicated Jastrow factors are available.
We present a perturbative treatment of Jastrow-type correlation factors which focuses on an accurate description of short-range correlations. Our approach is closely related to coupled cluster perturbation theory with the essential difference that we start from a variational formulation for the energy. Such kind of perturbation theory is especially suited for multiscale bases, like wavelets, which provide sparse representations for Jatrow factors. Envisaged applications in solid state physics are confined many-particle systems like electrons or multi excitons in quantum dots. The resulting Jastrow factors can be further used as trial wavefunctions in quantum Monte Carlo calculations for these systems. First applications to a screened homogeneous Fermi gas model demonstrate that already first order Jastrow factors recover 95 % of the correlation energy in variational Monte Carlo calculations over a fairly large range of densities and screening parameters. The corresponding second and third order perturbation energies turned out to be more sensitive to the specific choice of the model parameters. Furthermore, we have compared our first order Jastrow factors with those obtained from Fermi hypernetted chain calculations, where excellent agreement at short and intermediate inter-particle distances has been observed. 1
Standard analytical construction of the many-body wave function of interacting particles in one dimension, beyond mean-field theory, is based on the Jastrow approach. The many-body interacting ground state is build up from the ground state of the non-interacting system and the product of solutions of the corresponding interacting two-body problem. However, this is possible only if the center-of-mass motion is decoupled from the mutual interactions. In our work, based on the general constraints given by contact nature of the atom-atom interactions, we present an alternative approach to the standard construction of the \textit{pair-correlation} wave-function. Within the proposed ansatz, we study the many-body properties of trapped bosons as well as fermionic mixtures and we compare these predictions with the exact diagonalization approach in a wide range of particle numbers, interaction strengths, and different trapping potentials.
We present a perturbative treatment of Jastrow-type correlation factors which focus on an accurate description of short-range correlations. Our approach is closely related to coupled cluster perturbation theory with the essential difference that we start from a variational formulation for the energy. Such kind of perturbation theory is especially suited for multiscale bases, such as wavelets, which provide sparse representations for Jastrow factors. Envisaged applications in solid-state physics are confined many-particle systems such as electrons or multiexcitons in quantum dots. The resulting Jastrow factors can be further used as trial wave functions in quantum Monte Carlo calculations for these systems. First applications to a screened homogeneous Fermi gas model demonstrate that first-order Jastrow factors already recover 95% of the correlation energy in variational Monte Carlo calculations over a fairly large range of densities and screening parameters. The corresponding second- and third-order perturbation energies turned out to be more sensitive to the specific choice of the model parameters. Furthermore, we have compared our first-order Jastrow factors with those obtained from Fermi hypernetted chain calculations, where excellent agreement at short and intermediate interparticle distances has been observed.
Standard analytical construction of the many-body wave function of interacting particles in one dimension, beyond mean-field theory, is based on the Jastrow approach. The many-body interacting ground state is build up from the ground state of the non-interacting system and the product of solutions of the corresponding interacting two-body problem. However, this is possible only if the center-of-mass motion is decoupled from the mutual interactions. In our work, based on the general constraints given by contact nature of the atom-atom interactions, we present an alternative approach to the standard construction of the pair-correlation wave function. Within the proposed ansatz, we study the many-body properties of trapped bosons as well as fermionic mixtures and we compare these predictions with the exact diagonalization approach in a wide range of particle numbers, interaction strengths, and different trapping potentials.