  The negatively charged silicon vacancy [V$_\text{Si}(-)$] in silicon carbide
(SiC) is a paramagnetic and optically active defect in hexagonal SiC.
V$_\text{Si}(-)$ defect possesses $S = 3/2$ spin with long spin coherence time
and can be optically manipulated even at room temperature. Recently, electron
spin resonance signals have been observed besides the signals associated with
the V$_\text{Si}(-)$ defects in the 4H polytype of SiC. The corresponding
centers share akin properties to those of the V$_\text{Si}(-)$ defects and thus
they may be promising candidates for quantum technology applications. However,
the exact origin of the new signals is unknown. In this paper we report
V$_\text{Si}(-)$-related pair defect models as possible candidates for the
unknown centers. We determine the corresponding electronic structures and
magneto-optical properties as obtained by density functional theory (DFT)
calculations. We propose models for the recently observed electron paramagnetic
resonance centers with predicting their optical signals for identification in
future experiments.
