Real vs complex spherical harmonics for hexagonal symmetry

In summary, the conversation discusses the use of real and complex spherical harmonics for hexagonal symmetry and their association with a finite Lz. The position representation of an eigenvector of Lz is a standard complex spherical harmonic, with a corresponding expression in spherical coordinates. The question of any relation between crystal symmetry and these harmonics is raised, as well as a method for determining their superiority.
  • #1
Junaidjami
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TL;DR Summary
Orbital analysis of magnetic anisotropy energy using second order perturbation theory for hexagonal symmetry
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Are real spherical harmonics better than complex spherical harmonics for hexagonal symmetry, which are
directly associated to a finite Lz?
 
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  • #2
An eigenvector of ##L_z## in position representation is a standard complex spherical harmonic, i.e.,
$$\text{Y}_{lm}=P_{lm}[\cos(\vartheta)] \exp(\mathrm{i} m \varphi).$$
Note that in spherical coordinates the position representation of ##\hat{L}_z## reads
$$\hat{L}_z=-\mathrm{i} \hbar \partial_{\varphi}.$$
 
  • #3
vanhees71 said:
An eigenvector of ##L_z## in position representation is a standard complex spherical harmonic, i.e.,
$$\text{Y}_{lm}=P_{lm}[\cos(\vartheta)] \exp(\mathrm{i} m \varphi).$$
Note that in spherical coordinates the position representation of ##\hat{L}_z## reads
$$\hat{L}_z=-\mathrm{i} \hbar \partial_{\varphi}.$$

vanhees71 said:
Is there any relation between the crystal symmetry and real/complex spherical harmonics? And is there a way to judge the superiority of one over the other?
 

FAQ: Real vs complex spherical harmonics for hexagonal symmetry

What are spherical harmonics and how are they used in hexagonal symmetry?

Spherical harmonics are mathematical functions that describe the angular part of a function defined on the surface of a sphere. They are used in various fields, including quantum mechanics, electromagnetism, and computer graphics. In the context of hexagonal symmetry, spherical harmonics help in representing physical properties and wave functions that exhibit this specific type of symmetry, providing a convenient basis for solving related problems.

What is the difference between real and complex spherical harmonics?

Complex spherical harmonics are the standard form and are defined using complex exponentials, which makes them suitable for problems with rotational symmetry. Real spherical harmonics, on the other hand, are linear combinations of complex spherical harmonics that result in real-valued functions. Real spherical harmonics are often preferred in applications where the underlying physical quantities are real, such as in certain crystallographic and solid-state physics problems.

Why might one choose real spherical harmonics over complex spherical harmonics for hexagonal symmetry?

Real spherical harmonics are often chosen over complex ones for hexagonal symmetry because they can simplify the mathematical treatment of problems where the physical quantities are real-valued. Additionally, real spherical harmonics can sometimes lead to more intuitive interpretations and easier computational implementations in these scenarios.

How do real spherical harmonics simplify computations in hexagonal symmetry?

Real spherical harmonics can simplify computations by reducing the complexity involved in dealing with complex numbers. For hexagonal symmetry, the use of real spherical harmonics can lead to more straightforward expressions and can make it easier to enforce symmetry constraints. This simplification can be particularly beneficial in numerical simulations and analytical calculations.

Can both real and complex spherical harmonics be used interchangeably for hexagonal symmetry problems?

In principle, both real and complex spherical harmonics can be used to solve problems with hexagonal symmetry, as they form equivalent bases for representing functions on the sphere. However, the choice between them depends on the specific requirements of the problem, such as whether the physical quantities are real or complex, and the desired simplicity of the resulting expressions. While they are mathematically interchangeable, practical considerations often guide the choice of one over the other.

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