Minor: improved bohr_to_angstrom in constants

Author: alongd

arc/constants.pxd

@@ -1 +1 @@
-cdef double pi, Na, kB, R, h, hbar, c, e, m_e, m_p, m_n, amu, a0, E_h, F, E_h_kJmol, bohr_to_angstrom
+cdef double pi, Na, kB, R, h, hbar, c, e, m_e, m_p, m_n, amu, a0, bohr_to_angstrom, E_h, F, E_h_kJmol

arc/constants.py

@@ -41,6 +41,7 @@
 
 #: The Bohr radius :math:`a_0` in :math:`\mathrm{m}`
 a0 = 5.2917721092e-11
+bohr_to_angstrom = a0 * 1e10
 
 #: The atomic mass unit in :math:`\mathrm{kg}`
 amu = 1.660538921e-27
@@ -78,8 +79,6 @@
 #: Vacuum permittivity
 epsilon_0 = 8.8541878128
 
-bohr_to_angstrom = 0.529177
-
 # Cython does not automatically place module-level variables into the module
 # symbol table when in compiled mode, so we must do this manually so that we
 # can use the constants from both Cython and regular Python code